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...

Stereo rendering has been moved again to Begin3dMode() and End3dMode(),
it has some limitations but makes more sense...

Now it's easier for the user! Just init Oculus device and get stereo
rendering!

Redesigned rlgl usage:
- rlViewport() must be called by user
- Internal projection/modelview matrices must be setup by user

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

If Oculus device is not available or not initialized correctly,
simulated VR view is generated using stereo-rendering and distortion

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

Internal modelview and projection matrices can be replaced before
drawing.

This is a first step toward a bigger project. Some modules could be
ported to header-only to be used as standalone.

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.

Support render texture size different than screen size

Now shader maps use a generic naming convention for any kind of texture
maps (not only diffuse, normal or specular). Useful for custom shaders.

- 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.

Improved materials

- Renamed some functions for consistency (default buffers)
- Removed mystrdup() function (implemented inline)
- Renamed TextFileRead() to ReadTextFile()