strings - replace about.md file with concept files (exercism#2348)

* Pre-populate strings concept's about.md file from after.md file

* Pre-populate strings concept's links.json file from after.md file

* strings - Remove after.md document

* Apply suggestions from code review

Removed exercise specific info and added more detail on the concept.  Added and re-arranged links.

* [CI] Format code

Co-authored-by: BethanyG <[email protected]>
Co-authored-by: github-actions[bot] <github-actions[bot]@users.noreply.github.com>

Author: 3 people

concepts/strings/about.md

@@ -1 +1,61 @@
-TODO: add information on strings concept
+Pythons string type `str` can be very powerful. At its core, a `str` is an immutable [text sequence](https://docs.python.org/3/library/stdtypes.html#text-sequence-type-str) of [Unicode code points](https://stackoverflow.com/questions/27331819/whats-the-difference-between-a-character-a-code-point-a-glyph-and-a-grapheme). There is no separate "character" or "char" type in Python.
+
+Like any [sequence type](https://docs.python.org/3/library/stdtypes.html#sequence-types-list-tuple-range), code points or "characters" within a string can be referenced by 0-based index number, and can be copied in whole or in part via _slice notation_. Since there is no separate “character” type, indexing a string produces a new `str` of length 1 (_for example "exercism"[0] == "exercism"[0:1] == "e"_). Strings support all [common sequence operations](https://docs.python.org/3/library/stdtypes.html#common-sequence-operations), and individual code points or "characters" can be iterated through in a loop via `for item in`.
+
+For a deep dive on what information a `str` encodes (or, _"how does the computer know how to translate zeroes and ones into letters?"_), [this blog post is enduringly helpful][joel-on-text].
+
+Strings can be transformed by [various methods](https://docs.python.org/3/library/stdtypes.html#string-methods), split into letters/symbols, and joined together via [`.join()`](https://docs.python.org/3/library/stdtypes.html#str.join) or `+` to create larger strings . Due to their immutability, any transformations applied to a `str` return a new `str`.
+
+### Construction
+
+The simplest way to create a `str` literal is by delimiting it with `"` or `'`. Strings can also be written across multiple lines by using triple quotes (`"""` or `'''`) .
+
+````python
+single_quoted = 'Single quotes allow "double quoting" without "escape" characters.'
+
+double_quoted = "Double quotes allow embedded 'single quoting' without 'escape' characters".
+
+triple_quoted =  '''Three single quotes or double quotes in a row allow for multi-line string literals.  You will most often encounter these as "doc strings" or "doc tests" written just below the first line of a function or class definition.  They are often used with auto documentation tools.'''
+String literals that are part of a single expression and are separated only by white space are _implicitly concatenated_ into a single string literal:
+
+```python
+("I do not "
+"like "
+"green eggs and ham.") == "I do not like green eggs and ham."```
+
+
+Additionally,  [interpolated](https://en.wikipedia.org/wiki/String_interpolation) strings (`f-strings`) can be formed:
+
+```python
+my_name = "Praveen"
+
+intro_string = f"Hi! My name is {my_name}, and I'm happy to be here!"
+
+>>>print(intro_string)
+Hi! My name is Praveen, and I'm happy to be here!```
+
+Finally, the  [`str()` constructor](https://docs.python.org/3/library/stdtypes.html#str) can be used to create/coerce strings from other objects/types.  However, the `str` constructor _**will not iterate**_ through an object , so if something like a `list` of elements needs to be connected, `.join()` is a better option:
+
+```python
+>>> my_number = 675
+>>> str(my_number)
+'675'
+
+>>> my_list = ["hen", "egg", "rooster"]
+>>> str(my_list)
+"['hen', 'egg', 'rooster']"
+
+>>> ' '.join(my_list)
+'hen egg rooster'```
+
+
+### Formatting
+
+Python provides a rich set of tools for [formatting](https://docs.python.org/3/library/string.html#custom-string-formatting) and [templating](https://docs.python.org/3/library/string.html#template-strings) strings, as well as more sophisticated text processing through the [re (_regular expressions_)](https://docs.python.org/3/library/re.html), [difflib (_sequence comparison_)](https://docs.python.org/3/library/difflib.html), and [textwrap](https://docs.python.org/3/library/textwrap.html) modules.   For a great introduction to string formatting in Python, see [this post at Real Python](https://realpython.com/python-string-formatting/).
+
+For more details on string methods, see [Strings and Character Data in Python](https://realpython.com/python-strings/) at the same site.
+
+###  Related types and encodings
+
+In addition to `str` (a *text* sequence), Python has corresponding  [binary sequence types](https://docs.python.org/3/library/stdtypes.html#binaryseq) `bytes` (a *binary* sequence),  `bytearray` and `memoryview` for the efficient storage and handling of binary data.  Additionally, [Streams](https://docs.python.org/3/library/asyncio-stream.html#streams) allow sending and receiving binary data over a network connection without using callbacks.
+````

concepts/strings/links.json

@@ -1 +1,30 @@
-[]
+[
+  {
+    "url": "https://docs.python.org/3/library/stdtypes.html#text-sequence-type-str",
+    "description": "text sequence type - str"
+  },
+  {
+    "url": "https://docs.python.org/3/library/stdtypes.html#string-methods",
+    "description": "string methods"
+  },
+  {
+    "url": "https://docs.python.org/3/library/stdtypes.html#common-sequence-operations",
+    "description": "common sequence operations"
+  },
+  {
+    "url": "https://realpython.com/python-strings/",
+    "description": "string and character data in python"
+  },
+  {
+    "url": "https://realpython.com/python-string-formatting/",
+    "description": "string formatting best practices"
+  },
+  {
+    "url": "https://docs.python.org/3/library/string.html",
+    "description": "string - common string operations and formatting"
+  },
+  {
+    "url": "https://www.joelonsoftware.com/2003/10/08/the-absolute-minimum-every-software-developer-absolutely-positively-must-know-about-unicode-and-character-sets-no-excuses/",
+    "description": "joel-on-text"
+  }
+]