Shiny things 2

A few updates on the shading side this week. I've re implemented the Kelemen material (fixing a couple of embarrassing bugs along the way), and also added a basic metal material. It's using an old trick of doing per-rgb-component fresnel as a cheap approximation of a wavelength varying specular response for now. I'll go back in there and update to a better implementation later, but right now I want to move forward so I can get cracking on doing some texture work on this kitchen scene.

I still need to get UVs sorted for sub-d surfaces, and then look at using OpenImageIO for texture caching, as I'll be likely to run out of memory if I use my current naive way of keeping everything in memory.

Here are renders with a matte, kelemen and metal material, using the new sub-d code:

-Espen