[skip ci] Improve Readme guided by markdownlint

Author: martinmoene

README.md

@@ -3,6 +3,7 @@
 [![Language](https://img.shields.io/badge/C%2B%2B-98/11/14/17-blue.svg)](https://en.wikipedia.org/wiki/C%2B%2B#Standardization) [![License](https://img.shields.io/badge/license-BSL-blue.svg)](https://opensource.org/licenses/BSL-1.0) [![Build Status](https://travis-ci.org/martinmoene/string-view-lite.svg?branch=master)](https://travis-ci.org/martinmoene/string-view-lite) [![Build status](https://ci.appveyor.com/api/projects/status/1ha3wnxtam547m8p?svg=true)](https://ci.appveyor.com/project/martinmoene/string-view-lite) [![Version](https://badge.fury.io/gh/martinmoene%2Fstring-view-lite.svg)](https://github.com/martinmoene/string-view-lite/releases) [![download](https://img.shields.io/badge/latest-download-blue.svg)](https://github.com/martinmoene/string-view-lite/blob/master/include/nonstd/string_view.hpp) [![Conan](https://img.shields.io/badge/on-conan-blue.svg)](https://bintray.com/conan/conan-center/string-view-lite%3A_) [![Try it on wandbox](https://img.shields.io/badge/on-wandbox-blue.svg)](https://wandbox.org/permlink/ZfX49QqynfuQikTX) [![Try it on godbolt online](https://img.shields.io/badge/on-godbolt-blue.svg)](https://godbolt.org/z/YtxnAn)
 
 **Contents**  
+
 - [Example usage](#example-usage)
 - [In a nutshell](#in-a-nutshell)
 - [License](#license)
@@ -16,8 +17,7 @@
 - [Appendix](#appendix)
 
 
-Example usage
--------------
+## Example usage
 
 ```Cpp
 #include "nonstd/string_view.hpp"
@@ -26,7 +26,7 @@ Example usage
 using namespace std::literals;
 using namespace nonstd::literals;
 using namespace nonstd;
-    
+
 void write( string_view sv )
 {
     std::cout << sv;
@@ -41,30 +41,27 @@ int main()
 ```
 
 ### Compile and run
-```
+
+```Text
 prompt> g++ -Wall -std=c++14 -I../include/ -o 01-basic.exe 01-basic.cpp && 01-basic.exe
 hello, world!
 ```
 
-In a nutshell
----------------
+## In a nutshell
+
 **string-view lite** is a single-file header-only library to provide a non-owning reference to a string. The library provides a [C++17-like string_view](http://en.cppreference.com/w/cpp/string/basic_string_view) for use with C++98 and later. If available, `std::string_view` is used, unless [configured otherwise](#configuration).
 
 **Features and properties of string-view lite** are ease of installation (single header), freedom of dependencies other than the standard library. To mimic C++17-like cooperation with `std::string`, `nonstd::string_view` provides several non-standard conversion functions. These functions may be [omitted via configuration](#configuration).
 
+## License
 
-License
--------
 *string-view lite* is distributed under the [Boost Software License](LICENSE.txt).
- 
 
-Dependencies
-------------
-*string-view lite* has no other dependencies than the [C++ standard library](http://en.cppreference.com/w/cpp/header).
+## Dependencies
 
+*string-view lite* has no other dependencies than the [C++ standard library](http://en.cppreference.com/w/cpp/header).
 
-Installation
-------------
+## Installation
 
 *string-view lite* is a single-file header-only library. Put `string_view.hpp` in the [include](include) folder directly into the project source tree or somewhere reachable from your project.
 
@@ -83,22 +80,20 @@ Or, if you use the [conan package manager](https://www.conan.io/), follow these
 
         conan install
 
-
-Synopsis
---------
+## Synopsis
 
 **Contents**  
 [Documentation of `std::string_view`](#stdstring_view)  
 [C++20 extensions](#c20-extensions)  
 [Non-standard extensions](#non-standard-extensions)  
 [Configuration](#configuration)    
 
-Documentation of `std::string_view`
------------------------------------
+## Documentation of `std::string_view`
+
 Depending on the compiler and C++-standard used, `nonstd::string_view` behaves less or more like `std::string_view`. To get an idea of the capabilities of `nonstd::string_view` with your configuration, look at the output of the [tests](test/string_view.t.cpp), issuing `string-view-lite.t --pass @`. For `std::string_view`, see its [documentation at cppreference](http://en.cppreference.com/w/cpp/string/basic_string_view).  
 
-C++20 extensions
-----------------
+## C++20 extensions
+
 *string_view-lite* provides the following C++20 *extensions*.
 
 - *[[nodiscard]]* constexpr bool **empty**() const noexcept;
@@ -110,18 +105,20 @@ C++20 extensions
 - constexpr bool ***ends_with***( CharT const * s ) const;  // (3)
 
 Note: [[nodiscard]], constexpr and noexcept if available.
-     
-Non-standard extensions
------------------------
+
+## Non-standard extensions
+
 ### `string_view` literals `sv` and `_sv`
+
 clang compilers do not allow to write `auto sv = "..."sv` with *string-view lite* under C++11. To still provide a literal operator that can be used in that case, *string-view lite* also provides `_sv`. See section [Configuration](#configuration) for how to control the presence of these operators.
 
 The literal operators are declared in the namespace `nonstd::literals::string_view_literals`, where both `literals` and `string_view_literals` are inline namespaces, if supported. Access to these operators can be gained with using namespace `nonstd::literals`, using namespace `nonstd::string_view_literals`, and using namespace `nonstd::literals::string_view_literals`. If inline namespaces are not supported by the compiler, only the latter form is available.
 
 ### Cooperation between `std::string` and `nonstd::string_view`
+
 *string-view lite* can provide several methods and free functions to mimic the cooperation between `std::string` and  `nonstd::string_view` that exists in C++17. See the table below. Several macros allow you to control the presence of these functions, see section [Configuration](#configuration).
 
-| Kind                  | Std   | Function or method |                                       
+| Kind                  | Std   | Function or method |
 |-----------------------|-------|--------------------|
 | **Free functions**    |&nbsp; | macro `nssv_CONFIG_CONVERSION_STD_STRING_FREE_FUNCTIONS`|
 | **`std::string_view`**|&nbsp; | &nbsp; |
@@ -153,16 +150,15 @@ The literal operators are declared in the namespace `nonstd::literals::string_vi
 | &nbsp;                |&nbsp; | constexpr u32string_view operator "" **_sv**( const char32_t* str, size_t len ) noexcept; |
 | &nbsp;                |&nbsp; | constexpr wstring_view operator "" **_sv**( const wchar_t* str, size_t len ) noexcept; |
 
-
-Configuration
--------------
+## Configuration
 
 ### Standard selection macro
 
 \-D<b>nssv\_CPLUSPLUS</b>=199711L  
 Define this macro to override the auto-detection of the supported C++ standard, if your compiler does not set the `__cpluplus` macro correctly.
 
 ### Select `std::string_view` or `nonstd::string_view`
+
 At default, *string-view lite* uses `std::string_view` if it is available and lets you use it via namespace `nonstd`. You can however override this default and explicitly request to use `std::string_view` as `nonstd::string_view` or use string-view lite's `nonstd::string_view` via the following macros.
 
 -D<b>nssv\_CONFIG\_SELECT\_STRING_VIEW</b>=nssv_STRING_VIEW_DEFAULT  
@@ -171,6 +167,7 @@ Define this to `nssv_STRING_VIEW_STD` to select `std::string_view` as `nonstd::s
 Note: <b>nssv_CONFIG_SELECT_STD_STRING_VIEW</b> and <b>nssv_CONFIG_SELECT_NONSTD_STRING_VIEW</b> are deprecated and have been removed.
 
 ### Disable exceptions
+
 -D<b>nssv\_CONFIG\_NO\_EXCEPTIONS</b>=0
 Define this to 1 if you want to compile without exceptions. If not defined, the header tries and detect if exceptions have been disabled (e.g. via `-fno-exceptions`). Default is undefined.
 
@@ -183,6 +180,7 @@ Define this to 1 to provide literal operator `sv` to create a `string_view` from
 Define this to 0 to omit literal operator `_sv` to create a `string_view` from a literal string. Default is 1.
 
 ### Omit cooperation between `std::string`&ndash;`nonstd::string_view`
+
 At default, *string-view lite* provides several methods and free functions to mimic the cooperation between `std::string` and  `nonstd::string_view` (or `std::string_view`) that exists in C++17. See section [Non-standard extensions](#non-standard-extensions). The following macros allow you to control the presence of these functions.
 
 -D<b>nssv_CONFIG_CONVERSION_STD_STRING</b>=1  
@@ -194,9 +192,8 @@ Define this to 1 to provide `std::string`&ndash; `nonstd::string_view` interoper
 -D<b>nssv_CONFIG_CONVERSION_STD_STRING_FREE_FUNCTIONS</b>=1  
 Define this to 1 to provide `std::string`&ndash; `nonstd::string_view` interoperability via free functions, define it to 0 to omit all said functions. This also controls the presence of these function if `std::string_view` is used. Default is undefined.
 
+## Reported to work with
 
-Reported to work with
----------------------
 The table below mentions the compiler versions *string-view lite* is reported to work with.
 
 OS        | Compiler   | Versions |
@@ -208,9 +205,8 @@ GNU/Linux | Clang/LLVM | 3.5 - 6.0  |
 &nbsp;    | GCC        | 4.8 - 8 |
 OS X      | Clang/LLVM | Xcode 6, Xcode 7, Xcode 8, Xcode 9 |
 
+## Building the tests
 
-Building the tests
-------------------
 To build the tests you need:
 
 - [CMake](http://cmake.org), version 3.0 or later to be installed and in your PATH.
@@ -241,28 +237,29 @@ Here we use c:\string-view-lite\build-win-x86-vc10.
 
 All tests should pass, indicating your platform is supported and you are ready to use *string-view lite*.
 
+## Other implementations of string_view
 
-Other implementations of string_view
-------------------------------------
 - Marshall Clow. [string_view implementation for libc++](https://github.com/mclow/string_view). GitHub.
 - LLVM libc++. [string_view](https://llvm.org/svn/llvm-project/libcxx/trunk/include/string_view). GitHub.
 - Matthew Rodusek's, @bitwizeshift. [string_view Standalone](https://github.com/bitwizeshift/string_view-standalone). GitHub.
 - @satoren. [string_view for C++03 C++11 C++14](https://github.com/satoren/string_view). GitHub.
 - Google Abseil [string_view](https://github.com/abseil/abseil-cpp/tree/master/absl/strings) (non-templated).
 - [Search _string view c++_ on GitHub](https://github.com/search?l=C%2B%2B&q=string+view+c%2B%2B&type=Repositories&utf8=%E2%9C%93).
 
+## Notes and references
 
-Notes and references
---------------------
 *Interface and specification*
+
 - [string_view on cppreference](http://en.cppreference.com/w/cpp/string/basic_string_view).
 - [n4659 - C++17 Working Draft: string_view](http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2017/n4659.pdf#page=780).
 
 *Presentations*
+
 - Marshall Clow. [string_view - when to use it, and when not](https://cppcon2015.sched.com/event/3vch/stringview-when-to-use-it-and-when-not?iframe=yes&w=700&sidebar=yes&bg=no#). CppCon 2015. [video](https://youtu.be/H9gAaNRoon4), [slides](https://github.com/CppCon/CppCon2015/blob/master/Presentations/string_view/string_view%20-%20Marshall%20Clow%20-%20CppCon%202015.pdf).
 - Neil MacIntosh. [A few good types: Evolving array_view and string_view for safe C++ code](https://cppcon2015.sched.com/event/3vbQ/a-few-good-types-evolving-arrayview-and-stringview-for-safe-c-code). CppCon 2015. [video](https://youtu.be/C4Z3c4Sv52U), [slides](https://github.com/CppCon/CppCon2015/blob/master/Presentations/A%20Few%20Good%20Types/A%20Few%20Good%20Types%20-%20Neil%20MacIntosh%20-%20CppCon%202015.pdf).
 
 *Proposals*
+
 - Jeffrey Yasskin. [n3334 - Proposing array_ref<T> and string_ref](https://wg21.link/n3334). 2012.
 - Jeffrey Yasskin. [n3921 - string_view: a non-owning reference to a string, revision 7](http://wg21.link/n3921). **Adopted 2014-02**.
 - Alisdair Meredith. [n4288 - Strike string_view::clear from Library Fundamentals](http://wg21.link/n4288). **Adopted 2014-11**.
@@ -274,17 +271,15 @@ Notes and references
 - Peter Sommerlad. [p0506 - use string_view for library function parameters instead of const string &/const char *](http://wg21.link/p0506). 2017.
 - Daniel Krugler. [wg2946 - LWG 2758's resolution missed further corrections](https://wg21.link/lwg2946). 2017.
 
-
-Appendix
---------
+## Appendix
 
 ### A.1 Compile-time information
 
 The version of *string-view lite* is available via tag `[.version]`. The following tags are available for information on the compiler and on the C++ standard library used: `[.compiler]`, `[.stdc++]`, `[.stdlanguage]` and `[.stdlibrary]`.
 
 ### A.2 string-view lite test specification
 
-```
+```Text
 string_view: Allows to default construct an empty string_view
 string_view: Allows to construct from pointer and size
 string_view: Allows to construct from C-string