Some other tweaks...

Now it should be coherent with OpenGL math standards

SetMaterialTexture() and UnsetMaterialTexture()... too shader
dependant...

Corrected compilation for OpenGL 1.1
Review mesh data uploading to GPU

Moved PBR material loading to example, right decision?

...to avoid possible conflicting symbols

Combine it with transform introduced as function parameters

Replaced old GetExtension() function
Make IsFileExtension() public to the API

Working in modules configuration flags...

Lighting is implemented as a raylib example now

Function names, code formatting...

Start removing old rRES functions.

Correcting details that pop-up when testing the different platforms

Function was inefficient and should be rewritten from scratch, it
probably neither belongs to this module but an example...

raylib uses spaces between '+' and '-' signs but not between '*' and '/'
signs, it's a chosen convention

LoadOBJ can now load objects with having no texture coordinates or
objects having texture coordinates specified as tuples.

This fix allows GenMeshCubicmap() to create cubic maps having cells of
arbitrary sizes.

This function needs to be redesigned or removed...

It's more educational to go through new material system, so, I decide to
remove this function to avoid students confusion...

To get it, use GetDefaultTexture()