Simplified some parts and reviewed for a correct computation of matrices, considering stereo render view/projection per eye transformations

Use fabsf() instead of abs()

shaders_rlgl_mesh_instanced -> shaders_mesh_instancing

* CheckCollisionPointTriangle

* New feature proposal to existing collision detection routines.
It checks if point [point] belongs to line created between two points [p1] and [p2] with defined margin in pixels[threshold].
1693

As a bonus, stereo render is compatible with mesh instancing now!

Co-authored-by: Carlos Hernandez Barbera <carloshdezbarbera@gmail.com>

rlgl module has been completely redesigned to move Mesh/Material structures to [models] module. Still some work to do, broken elements:
 - [models] OpenGL 1.1 mesh rendering: DrawMesh()
 - [models] Mesh Instancing: DrawMeshInstanced()
 - [models] Stereo rendering: DrawMesh()
 - [models] GL_FLOAT, GL_UNSIGNED_INT exposed
 - [models] GenMeshCustom()
 - [rlgl] GenTexture*() functions removal?

* adds DrawTexturedPoly with example

* the actual example ... ahem

* moved DrawTexturePoly to textures function and example
NB function name changed to fit with other DrawTextureXXX functions
(no "d" )

Co-authored-by: codifies <you@example.com>

Co-authored-by: Jeffery Myers <JefMyers@blizzard.com>

This is a very simple and specific implementation that should be better addressed by the users

Function analyzed using RenderDoc. It's a complex function and could require many triangles for the corners but it seems overall it's quite optimized!

- The vertices did not map to where I expected causing rotation to be
off by 90 degrees. I reorganized the vertices making it easier to
reason about which fixes this.
- The order for drawing is now topLeft, bottomLeft, bottomRight,
topRight.

The Raylib root Makefile for PLATFORM=PLATFORM_WEB is assumed to
run in Windows environments, which makes it incorrectly set the
PATH variable, so Linux (and possibly other) environments are not
able to find binaries from EMSDK_PATH.

Fix this by checking which PLATFORM_OS and configure PATH
accordingly.

* Fix some warnings in examples.

* cleanups from review

Co-authored-by: Jeffery Myers <JefMyers@blizzard.com>

Co-authored-by: Jeffery Myers <JefMyers@blizzard.com>

- Many functions renamed to follow rl*() convention
- Some internal functions exposed in the API
- Some functionality moved to other modules
- Reorganized all functions by categories
- Make sure it keeps working with OpenGL 1.1 and 2.1