`instance Monad Material where`

Sitting on my hands to avoid going full CPS on it (again)

#haskell

Textures are just `Material a` combinators concerned with producing stuff at hit points.

Since the Material is a Monad now, no need for special cases for colors and then another bunch of combinators for materials.
A sampler can be used to pick entire materials if needed.
(Ooops, I actually CPSd a little...)

#haskell