Anisotropix GGX work.
Merge branch 'master' into anisotropic_ggx
Added anisotropic GGX, small fixes and formatting.
Small improvements to MDF2 tests.
Small fixes.
Improved tests, fixed nans and other small changes.
Formatting fixes.
Merge pull request #466 from est77/anisotropic_ggx

Microfacet2 improvements and anisotropic GGX