Illum

This replaces pull request #61

Read specification modified to match our code here: MTL Specification

Now supports .mtl file illum modes:

0. Color
1. Diffuse
2. Diffuse + Specular
3. Diffuse + Specular + Reflection
4. Diffuse + Specular + Reflection + Transparency
5. Diffuse + FresnelSpecular + FresnelReflection
6. Diffuse + Specular + Reflection + Refraction
7. Diffuse + FresnelSpecular + FresnelReflection + FresnelRefraction
8. Diffuse + Specular + Reflection (asks for no-ray-tracing, ignore, fallback to 3)
9. Diffuse + Specular + Reflection + Transparency (asks for no-ray-tracing, ignore, fallback to 4)
10. None

Fresnel needs implementation

Modes:

0. Pass material color as value (no effects)
1. Diffuse filter only
2. Diffuse and Specular filters
3. Reflection (for mirrors)
4. Transparent (for non-refractive transparent materials)
5. Fallback to normal reflection mode. Now renders, but needs implementation of Fresnel for prettification.
6. Refraction (for refractive transparent materials)
7. *Fallback to normal refraction mode. Now renders, but needs implementation of Fresnel for prettification.
8. Defaults to 3
9. Defaults to 4
10. Always black