haskell: Completely removed the Group, Subset, and Element types, replacing
them with Group' a, Set a, and nothing, respectively
Groups/Ops.hs: Improved isAbelian
Changed some absolute imports in groups/*.py to relative imports
Renamed Groups/Types.hs to Groups/Type.hs and cleaned up haskell/TODO.txt
Updated haskell/tests for the new types
Updated a couple files in haskell/dev for the new types
Haskell: Updated `abelians` and moved it from dev/ back to Groups/Families.hs
Found & fixed a bug
Merge branch 'haskell2'