Some deep review of this shaders is required for optimization...

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

- 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.

- 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.