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.

Replaced Vector3 by direct values, easier to use and understand

Reason for removal: This function forces a specific Image data format, it copies data internally (it could be confusing and lead to memory leaks), it's redundant, there is a simpler alternative and raylib promotes using structures directly

Some internal defines have been exposed in config.h

* Implemented DrawTextureTiled()

* Example added

Probably there is a better way to do this but this is a temporary solution for backward compatibility

After multiple tests and lot of redesign, current implementation is the fastest one. It also considers several fast-paths for maximum speed!

WARNING: Some functions ADDED and some RENAMED:
- RENAMED: Fade() -> ColorAlpha() [Added #define for compatibility]
- ADDED: ColorAlphaBlend()
- ADDED: GetPixelColor()
- ADDED: SetPixelColor()

Trying a new optimization approach, some additional functions added, they will be probably exposed soon.

Despite all the effort put on function optimization, dealing with alpha blending is complex, considering src and dst could have different pixel format...

Optimized to avoid ImageCrop() calls, now we define the source image rectangle and we just copy that data over the new canvas.

Always using RGBA for now.

Further optimization, moving data line-by-line
Old optimization left for reference

Using ImageResizeCanvas()

Now uses GetImageAlphaBorder()

Avoid GetImageData() retrieval and free

Added several optimized options for future reference (if required)