REMOVED: DrawBillboardEx()

* Redesigned billboards - added rotation/pro functions

* updated parameters

Co-authored-by: nobytesgiven <nobytesigiven@github.com>

Co-authored-by: Lambert Wang <lambert.ww@gmail.com>

* Added support for additional mouse buttons

* Renamed mouse button enum

Co-authored-by: Lambert Wang <lambert.ww@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>

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

- 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

* Add loop functions for music files.
Tell xm tracker to loop tracker when loop state changes.
Don't let looped xm tracker streams restart, they are infinite
Use modulo to make time tracker for xm looped streams work correctly.

* Remove loop functions, set XM loop in update based on flag.
Formatting cleanups.

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

- Some rlgl functions have been moved to core
 - Some functions have been made internal to rlgl
 - rlgl functions prefixed with rl*()

Vr simulator has been moved to core module and completely redesigned. Now user is in charge of stereo-render fbo and also in full control of distortion shader. Code is a bit more complex but better aligned with other raylib examples.

Co-authored-by: Simon <simon@frithrah.com>

This function could be confusing depending on the context, it's better to let the user track the current active cursor

Now enum names are more consistent between them.

Just assigned a fixed memory size for custom Material parameters in case of being required, so we shouldn't worry about allocating/freeing them.

Some enums values have been renamed to be more consistent and also provide a more detailed description:
 - ShaderLocationIndex:    LOC_VERTEX_POSITION -> SHADER_SHADER_LOC_VERTEX_POSITION
 - ShaderUniformDataType:  UNIFORM_VEC2 -> SHADER_UNIFORM_VEC2
 - MaterialMapType: MAP_ALBEDO -> MATERIAL_MAP_ALBEDO
 - PixelFormat: UNCOMPRESSED_GRAYSCALE -> PIXELFORMAT_UNCOMPRESSED_GRAYSCALE

Removed memory allocation callbacks

NOTE: This feature is still under consideration and not complete.

RENAMED: TextureFilterMode values
RENAMED: TextureWrapMode values

RENAMED: CubemapLayoutType and NPatchType