map/reduce style run with monoidal reduce
grid zipping added and refactoring
removed old type-level functions not used anymore
unzipping grids
Merge branch 'master' of https://github.com/dorchard/ypnos into comonadic

Conflicts:
	src/Ypnos/Core/Combinators.lhs
	src/Ypnos/Core/Grid.lhs
No need for a dimension argument to fromDim. It can deduce from type.
Added indexing to the ListGrid class.
Clamp rather than Mirror actually seems to implement what we call mirror behaviour.
Some changes to make life work on GPU as well. We have uncovered some nastiness
the GPU we should have done earlier.
Stray `trace` got left in.