Corrects weird artifacts on web

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.