* Adds experimental support for automatically SQL query optimization via a `FlexFieldsFilterBackend`. Thanks ADR-007!
* Adds CircleCI config file. Thanks mikeIFTS!
* Moves declaration of `expandable_fields` to `Meta` class on serialzer for consistency with DRF (will continue to support declaration as class property)
* Python 2 is no longer supported. If you need Python 2 support, you can continue to use older versions of this package.