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

texture2D() is deprecated on GLSL 330

Now GLFW3 windows/context creation works ok and a sample red rectangle
has been drawn using rlgl. Next step is working in tracking
position/orientation maths and try to get a simple 3d scene...

NOTE: It requires a depth texture as input, it should be configured on
rlgl, by default RenderTexture (fbo) uses Depth Renderbuffer instead of
Depth Texture. Check rlglLoadRenderTexture()

Now it's possible to render to texture, old postprocessing system will
be removed on next raylib version.