Ah it's not that fancy yet
I'm so rusty in this area that it pains me. But I figured that if we have this as a working base we could always improve on it incrementally.
The somewhat ad-hoc sampling weighting scheme seems to work fairly well, and in general the speed hit seems to be fairly modest compared to a plain glossy material.
I'll clean up the code so I can push it. One thing I struggle with is naming and such... I added SchlickGlossyBRDF to the "schlickbrdf" file and GlossyCoating to the "glossy2" file. Since they're so similar to their "cousins" I figured it was best to keep them in the same files, but I could split them up. Please let me know if I should change this, easier to do it before I commit.
May contain traces of nuts.