Latest raylib 1.6

Trying to find the best way to integrate Oculus support into raylib,
making it easy for the user...

Internal modelview and projection matrices can be replaced before
drawing.

To avoid additional dependencies

Moved AudioError enum inside audio.c

The only thing I did not change was the _g for globals. Is there any
other way we can mark globals?

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

It tints all fragments, ignores lighting. Useful for some features like
feedback (damage color, ...).

Scaling normal depth (y axis) makes disappear the specular of
fragments... So I think it can be removed, it is not a very
useful/important attribute.

Draw3DCircle is useful to draw point lights radius.

- 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.

- Ambient and lambert lighting added.
- Ambient and diffuse colors linked to standard shader.
- Single light linked to standard shader.
- LoadStandardMaterial() and depending functions added.

Improved materials

Depending on mesh data, it can be loaded and default vertex attribute
location points are set, including colors, tangents and texcoords2