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.

In standard shader, material glossiness is a value from 0 to 1000 like
in MLT files. So, it doesn't need to be normalized.

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

...on model drawing

Material glossiness is a float type value...

Improved materials

Only works when raylib is installed on windows system.

_g naming convention for globals, new error exit numbers.

Keep asking myself why I maintain this rendering path... -___-

now it works

Not tested yet

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