Support render texture size different than screen size

I made this for some others I am now working with

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

It seems there are some problems with DrawLights()

Standard Lighting (2/3)

- 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.

remove user-specific ant files

fix example

- fix gamepad axis query in example broken by db4585b Improved gamepad support

- 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

MTL loading shininess to material glossiness

Material glossiness is a float type value...

Improved materials

Redesign audio system to support multiple mix channels

Only works when raylib is installed on windows system.

texture2D() is deprecated on GLSL 330

Fix building examples on OSX

_g naming convention for globals, new error exit numbers.