Replaced: Returns -> Get

- Dividing by height instead of width results in missing parts of the image.

Removed functions from rlgl module.

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>

- 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.

- 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

* Optimize DrawTexturePro and DrawRectanglePro transformations
- Add check so rotation is only applied if rotation != 0.0f.
- Replace matrix usage by calculating the vertex data directly.

* Fix error with windows build and trim whitespace

Now enum names are more consistent between 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

This new flag allows omitting stdio.h library in case of a custom implementation is used.

RENAMED: TextureFilterMode values
RENAMED: TextureWrapMode values

RENAMED: CubemapLayoutType and NPatchType

* Don't use DrawRect to clear an image, a pixel loop is an order of magnitude faster.

* Update ImageDrawRectangle to be faster too.

Pefixing/Suffixing some data type identifier in the variables is not a convention used in raylib, just reviewed it for consistency...

Still, I kept the *Rec suffix in some functions.

This is a BREAKING CHANGE!

To address the linked issue, several functions have been renamed and couterpart functions have been created to free loaded memory:
 - RENAMED: GetImageData() -> LoadImageColors()
 - RENAMED: GetImagePalette() -> LoadImagePalette()
 - RENAMED: GetWaveData() -> LoadWaveSamples()
 - ADDED: UnloadImageColors()
 - ADDED: UnloadImagePalette()
 - ADDED: UnloadWaveSamples()

Since I don't think the purpose of raylib is to save space compressing image, I think it could be a good idea to keep quality from 90 to 100.

Let the advance users manage it as they want...

Required to attach multiple color textures and multiple cubemap faces

This redesign allows more flexibility when creating RenderTexture and a simplification (and hopefully removal) of `GenTexture*()` functions, that should not belong to this model but the user code, due to the use of custom shaders.

Also, this new API opens the door for a possible GBuffers type and advance rendering possibilities...

Some functions of the API have been also simplified or even removed.

rlgl module can be used as an standalone library, so, a version for the library has been added: v3.1.0, matching current raylib version.