------
* Refactored Fields:
Fields have been refactored, for better maintenance. There should be no change for most users.
- More accurate auto-completion.
- Fields now contain their own SQL schema by dialect, which significantly simplifies adding field types.
- ``describe_model()`` now returns the DB type, and dialect overrides.
- ``JSONField`` will now automatically use ``python-rapidjson`` as an accelerator if it is available.
- ``DecimalField`` and aggregations on it, now behaves much more like expected on SQLite (256)
- Check whether charset name is valid for the MySQL connection (261)
- Default DB driver parameters are now applied consistently, if you use the URI schema or manual.