Corrected issue with sound playing (pop sound at the end)

Still a work in progress but it already works...
Current riqm API could be simplified...

This change allows rlgl.h usage as independent single-file header-only module... still some tweaks required, like removing GLAD dependency... required extensions could be manually loaded!

Also removed shader_distortion.h, embedded in rlgl.h

Note for me: Replace All is NOT your friend...

Added: data to CharInfo struct
Added: LoadFontData()
Added: GenImageFontAtlas()
Removed: LoadFontEx()
Removed: LoadTTF() [internal]
Some code tweaks

Reviewed: GetImageData()
Reviewed: ImageFormat()

- Preparing MP3 files support
- Jumped version to raylib 2.0-dev (too many breaking changes...)

Note that only some lib versions have been updated

Not required any more!

Added: DrawRectangleGradientV()
Added: DrawRectangleGradientH()

SetWindowTitle()
GetExtension()

Moved function DrawRectangleT() from text module to shapes
Added some comments

Usefult to draw rectangles using default font texture

Exposed some raymath useful functions to raylib API

Moved PBR material loading to example, right decision?

...to avoid possible conflicting symbols

Namely:
- GenImageHorizontalV
- GenImageHorizontalH
- GenImageChecked
- GenImageWhiteNoise
- GenImageCellular

The gradient implementation may be a bit naive, for example it doesn't do any gamma correction.