variables context manager
isvar checks hashable before test for membership
remove reify_var
doctest for variables context manager
support for slice unify
unify registry functions for objects
clean unify/reify_slice
unique passes on unhashable objects
factor unify -> unify and unifymore

Moved unify/reify_object/slice to unifymore
more_unify_dispatch
object/with(variables) test
Merge pull request #22 from mrocklin/my-jaberg-slice

Unification of slices and convenience functions for object registration