add glsl preprocessor

[0x2A]

It might be useful to create a preprocessor for GLSL shader files. It causes a loss of compatibility for standard glsl code but it might be useful to have some #include or #pragma functionality. So this should it make possible to create some reusable shader code like default lighting or headers (for example the in vec3 vertPosition ... uniforms), so its easier to create custom shaders.

[0x2A]

_default_vertex_inputs_ and _reduced_vertex_inputs_ macros are now implemented.

_default_vertex_inputs_ adds:

 in layout(location=MODEL_NORMAL_LOCATION) vec3 vertexNormal;
 in layout(location=MODEL_TEXCOORD_LOCATION) vec2 vertexUV;
 in layout(location=MODEL_VERTEX_COLOR_LOCATION) vec4 vertexColor;
 in layout(location=MODEL_TANGENT_LOCATION) vec3 vertexTangent;

and _reduced_vertex_inputs_ adds:

in layout(location=MODEL_VERTEX_LOCATION) vec3 vertexPosition;
in layout(location=MODEL_TEXCOORD_LOCATION) vec2 vertexUV;
in layout(location=MODEL_VERTEX_COLOR_LOCATION) vec4 vertexColor;

to shader code