New HStore field in django.postgres: steal some improvements?

[nemesis]

https://github.com/djangonauts/django-hstore/issues/76

How about stealing some improvements from this PR?
django/django#3219

:-)

It looks like the implementation is intentionally simple so to avoid complex code to achieve certain features.

So it probably make sense to take some improvements back into django-hstore.

Then if in PostgreSQL, the binary json type will really be merged with the hstore 2.0 features as it was announced few months ago, it could make sense to implement support for this new feature (binary json with hstore lookups and indexes) directly in this package which is already widely used.