Make ValueQuoter objects equal if their repr() are equal.

This makes model instances which have quoted values to equal in an
intuitive manner.
Merge branch 'valuequoter-comparison' of github.com:dokai/cqlengine into pull-77
updating value quoter equal function to compare values not repr
updating equality operations to stop relying on the to_database dictionary conversion
renaming as_dict to _as_dict
updating changelog and version