Perceptually Linear Color Spaces

David pointed out that my pull request should be directed to the devel branch. I just cleaned up a few things and made the transformMatrix variables 'static const' as per Graham's suggestion. Regarding moving the new #include statements into al_Color.cpp, I tried this but I ran into some problems in my test setup when I tried to compile so I'm leaving it as-is for now (this might have just be due to how I've included the files in my test project, though).