Micro facets

In this weeks episode I've been cleaning up my material code. I've changed the microfacet distribution of my specular model to the modified Beckmann distribution suggested by Kelemen et al, and made the interface a bit more generic than before, so I can extend it to a bsdf next when I add subsurface scattering - and later plug in a shading engine to support varying parameters through texturing, procedural patterns etc.

For now, here's a pink buddah. 2048x2048, 4k samples per pixel, 10 light bounces.

-Espen