Initial version of Django kmatch

@wilduck @micahhausler @wesokes this is the initial version of Django kmatch. It is meant to serve as a Django wrapper around kmatch. While it only supports a custom model field, I think it could eventually support an extended K object that can do matching on Django models.

Anyways, it was fairly complex to make a custom field that inherited a JSONField. The JSONField field creates its own meta class and also overrides a different method than to_python to do conversion. After digging in the JSONField code, it was more obvious what needed to be overridden.

Docs and everything should be good to go