Use signal and command to provide the same capability of the custom database backend.

Current custom database backend does 3 things:

 1. Call register_hstore for each connection.
 2. Install hstore contrib for every database created.
 3. Create index for hstore field.

This commit use connection_created to do the first two things. And sqlhstoreindexes command to do the third thing.

Plus this commit also fixed an issue when using south to add an hstore field with a default value.
Fall back to JsonField when using sqlite database.
Fix the bug that one has to install psycopg2 to use the sqlite database
Work in progress Json dict support.
Add json key-value support. Now we could store numbers, dicts and arrays in HStoreField.
Bugfix for processing normal keys.
Fixed the south migration bug.
Fix the print HStoreDict bug.
Merge pull request #1 from jezdez/master

blah
Temporary bugfix.

Due to a couple of bugs, json objects are never loaded from
dict values. This fix always tries to load json values.
Merge pull request #2 from AsymmetricVentures/backend-removal

Backend removal
Make HStoreDict pickable

Connection is not pickable
Update documentation

Custom backend not needed anymore
Revert "Temporary bugfix."

This reverts commit a20e43e13e8d9a8a38d2eda131df009ca297aaee.
Test DictionaryField is pickable
Fix AttributeError

If self.connection is missing, an AttributeError is raised.
Got this error while using rest_framework, but still not found how
HStoreDict is missing of 'connection' attribute
Fix: wrong implementation of __getstate__ protocol
Merge https://github.com/AsymmetricVentures/django-hstore
Merge branch 'backend-removal'
Removed need of custom backend + cleanup + docs + more tests

Merge branch 'master' of https://github.com/cybercase/django-hstore

Conflicts:
	README.rst
	django_hstore/fields.py
	tests/django_hstore_tests/tests.py
	tests/runtests.py