Operate over global variable

Removed functions from rlgl module.

Avoid RLGL data dependency to allow moving the functions somewhere else

After some investigation, I came to the conclusion it's impossible to get a solution that works for all situations. Fullscreen mode on web depends on the browser, the canvas and also the desired scaling strategy of the user. Just choose a solution that fits me needs for now and let the user manage the canvas on their webs (hopefully not requiring ToggleFullscreen() call).

Also removed several useless related callbacks.

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.

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