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

...to align it with standard raylib code. Final goal would be having the
same code work for every platform with no changes...

Under design... looking for the easiest and most comprehensive way for
the user to use VR...

and remove static from PhysicsThread().

and add instructions in physac examples to run it successful.

and added PHYSAC_NO_THREADS define. Improved physac example drawing
frames per second in screen.

texture() doesn't exist in glsl 100, it must use texture2D().

Trying to simulate Oculus Rift CV1 rendering without the device... for
Debug pourposes.

Not functional yet...

Still working on the sample but almost finished. Some rlgl internals
redesign required and it will be ready!

Tint color could be applied to colDiffuse... but what's the best way?
Replace it? Multiply by? A point to think about...

Functions renamed to improve library consistency

- Added normal and specular maps to standard shader.
- Added full tint attribute to standard shader and material data type.
- Changed point light attenuation to radius.

...shader and updated example.

Support render texture size different than screen size

It seems there are some problems with DrawLights()

- 3 light types added (point, directional, spot).
- DrawLights() function added using line shapes.
- Standard lighting example added.
- Removed useless struct variables from material and light.
- Fixed light attributes dynamic locations errors.
- Standard vertex and fragment shaders temporally added until rewrite it
as char pointers in rlgl.
TODO:
- Add normal and specular maps calculations in standard shader.
- Add control structs to handle which attributes needs to be calculated
(textures, specular...).
- Adapt standard shader to version 110.
- Rewrite standard shader as char pointers in rlgl.

- fix gamepad axis query in example broken by db4585b Improved gamepad support