Initial attempt at making django_hstore work for django 1.7
added django 1.7 to .travis.yml
change import statement in tests
Added ``hints`` parameter to HStoreGeoQuerySet constructor for Django 1.7 compatibility
Django 1.7 compatible custom lookups for hstore comparison operators
Added custom classes for icontains and contains lookups
Alternative cast fix in HStoreContains
Added a bunch of tests for native lookups
Restores backwards compatibility with Django < 1.7
Python 3 compatibility fix
Restricted usage of custom lookups to instances of HStoreField
Additional tests for invalid values in custom lookups
Raise ValueError in WhereNode.make_atom if an empty list is passed as a parameter for contains and icontains lookups
Using `HstoreField.register_lookup` instead of `get_lookup` for custom 
lookups.
Removed useless db_type check in HStoreContains
updated VERSION to 1.2.3 + updated README
fix issues on psycopg2 backend + tests
 * run separate test suite with psycopg2 backend only
 * defer HSTORE registration in certain cases as suggested by @fabiocorneti in #34
 * clean up of some deprecation warnings