That way, a user needs only to touch a single file to configure what
features raylib is built with.
Include guards are left out intentionally, because config.h should only
be included in source files, not headers.

Later on, config.h can also define the raylib version (#461).

Added struct Vector4 for convenience

- Renamed enum TextureFormat to PixelFormat for consistency
- Added support for pixel format UNCOMPRESSED_R32
- Using GetPixelDataSize() where required

To be more generic and configurable

Requires some work, distortion shader could be move out of raylib to
example code...

Now it should be coherent with OpenGL math standards

Exposed some raymath useful functions to raylib API

...to avoid possible conflicting symbols

Moved to custom example, now raylib only supports simulated VR
rendering.
Oculus code was too device dependant... waiting for OpenXR.

texture.mipmaps value needs to be updated, so, texture must be passed by
reference instead of by value

...to avoid dynamic conditions on for loop (lightsCount) on standard
shader, it seems GLSL 100 doesn't support that feature... on some GPUs
like RaspberryPi...