doc fixes, added SVG import image

Author: skramm

docs/homog2d_manual.md

@@ -1097,7 +1097,8 @@ See [demo program](../misc/test_files/bg_test_1.cpp) that demonstrates that feat
 
 We follow here the traditional parametrization of ellipses:
 center point, semi-major (a) and semi-minor (b) distances, and angle between main axis and horizontal axis.
-Internally, it is stored as a conic in its matrix form (see [build options](#build_options) for details).
+Internally, it is stored as [a conic in its matrix form](https://en.wikipedia.org/wiki/Matrix_representation_of_conic_sections),
+see [build options](#build_options) for details on how this is handled.
 
 _Warning: support for ellipse is only partial at present, several features available with all the other primitives may not
 all be available for this type_
@@ -2104,6 +2105,10 @@ auto vcol2 = img::genRandomColors(10,100);    // return 10 random colors with va
 auto vcol3 = img::genRandomColors(10,30,150); // return 10 random colors with values in the range [30-150]
 ```
 
+You can then use these with the `setColor()` member function:
+```C++
+something.draw( image, img::DrawParams().setColor( vcol1.at(i) ) );
+```
 
 ### 8.5 - Drawing containers holding variant objects (runtime polymorphism)
 
@@ -2288,12 +2293,21 @@ auto data = visitor.get();
 ```
 
 The latter function returns a vector of polymorphic objects `CommonType`.
-This is a wrapper around a `std::variant`, on which the library provides some helper functions.
+This is a wrapper around a [`std::variant`](https://en.cppreference.com/w/cpp/utility/variant),
+on which the library provides some helper functions.
 See [RTP section](#section_rtp) on how to use this.
 This polymorphic behavior is kept optional,
-It is enabled only if symbol `HOMOG2D_ENABLE_VRTP` is defined
+it is enabled only if symbol `HOMOG2D_ENABLE_VRTP` is defined
 (which is automatically done if `HOMOG2D_USE_SVG_IMPORT` is defined).
 
+For safety, you can check if the file has been correctly read by testing the return value of the `LoadFile()` member function:
+```C++
+tinyxml2::XMLDocument doc;
+auto error = doc.LoadFile( "filename.svg" );
+if( err != tinyxml2::XML_SUCCESS )
+	FAILURE!
+```
+
 You can fetch the size of image in the SVG file (as `double`) with `getImgSize()`.
 However, this will throw if no size can be found, so you might consider using that in a "try/catch":
 ```C++
@@ -2349,9 +2363,14 @@ For example:
 <br>
 `$ BUILD/demo_svg_import docs/img/comparison_1.svg`
 
-The previous line imports a file that has been generated by this library, so to have comething more realistic, you can run this:
+The previous line imports a file that has been generated by this library, so to have something more realistic, you can run this:
 <br>
-`$ BUILD/demo_svg_import misc/test_files/France_Normandy.svg`
+`$ BUILD/demo_svg_import misc/test_files/France.svg`
+
+This will produce this image, with the bounding boxes of the different regions drawn with different colors:
+
+![import_demo_France](img/import_demo_France.svg)
+
 
 ## 11 - Technical details
 <a name="tech"></a>
@@ -2372,7 +2391,7 @@ For more details on the code, check [this page](homog2d_devinfo.md).
 
 A unit-test program is included, can be run locally and is also used by GitHub CI.
 It is uses the [Catch2](https://github.com/catchorg/Catch2) library.
-The Github CI (aka "Github Acionts") loads the 2.13.6 release.
+The Github CI (aka "Github Actions") loads the 2.13.6 release.
 It is build and run with `$ make test`
 The CI launches the tests with both Ubuntu 20 (gcc9.4) and Ubuntu 22, and also makes sure that the Microsoft C++ compiler is able to build the software
 (but it does not run the tests with it).
@@ -2388,7 +2407,7 @@ make test USE_TINYXML2=Y
 ```
 
 A second test target is included: `$ make testall`.
-It will build and run the test program 3 times, one for each numerical data
+It will build and run the tests programs 3 times, one for each numerical data
 type (`float`, `double`, and `long double`), through the symbol `HOMOG2D_INUMTYPE`.
 
 The test target also attempts to build the files in the folder `misc/no_build`.
@@ -2433,16 +2452,15 @@ If not defined, incorrect situations will throw a `std::runtime_error`.
 If defined, program will very likely crash in case an abnormal situation is encountered.
 - `HOMOG2D_NOWARNINGS`: on some situations, some warnings may be printed out to `stderr` (see below).
 Defining this symbol will disables this.
-Besides this build symbol, user code can silence all the warnings with `err:printWarnings() = false;`
+Besides this build symbol, user code can silence all the warnings with `err::printWarnings() = false;`
 (can be reactivated any time by passing `true`).
-- `HOMOG2D_OPTIMIZE_SPEED`: this option may be useful if you intend to to a lot of processing with ellipses, and you favor speed over memory.
+- `HOMOG2D_OPTIMIZE_SPEED`: this option may be useful if you intend to to a lot of processing with [ellipses](#p_ellipse), and you favor speed over memory.
 The default behavior for class `Ellipse` is to store only the homogeneous matrix representation (conic form),to minimize memory footprint.
 This drawback is that every time we need to access some parameter (say, center point), a lot of computations are required to get back to the "human-readable" values.
-With this option activated, each ellipse will store both representations, so access to values is faster.
+With this option activated, each ellipse will store **both** representations, so access to values is faster, but memory footprint will increase.
 For more on this, [see this page](homog2d_speed.md).
 - `HOMOG2D_ENABLE_PRTP`: enables pointer-based runtime polymorphism.
-This will add a common base class `rtp::Root` to all the geometric primitives.
-At present, runtime polymorphism is currently moving to a variant-based approach, see [RTP](#section_rtp) section.
+This will add a common base class `rtp::Root` to all the geometric primitives, see [RTP](#section_rtp) section.
 - `HOMOG2D_ENABLE_VRTP`: enables variant-based runtime polymorphism.
 This will add a class `rtp::CommonType` holding all the geometric primitives as a std::variant.
 See section [RTP](#section_rtp) for details.
@@ -2452,12 +2470,6 @@ While this shoudn't happen even with random data, numerical (floating-point) iss
 [read this for details](homog2d_qa.md#assert_trigger).
 
 
-**Situations that will generate a warning**
-
-* When computing the angle between two lines/segments, and that this requires the computation of `arccos()` of a value slightly above 1.
-Then the value 1.0 will be used instead, but a warning will be generated.
-* When importing a SVG file and an element in the file cannot be processed.
-
 
 ### 12 - Runtime Polymorphism
 <a name="section_rtp"></a>