Graphene-elastic

------
2019-09-04

- Fixes.
- Clean up.

-----
2019-09-03

- Added pagination.
- Documentation improvements.

-----
2019-09-02

- Tested default ordering backend.
- Documentation improvements.

-----
2019-09-01

- Ordering backend.
- Added more filter lookups.
- Minor fixes in existing filter lookups.
- Improved test coverage for the filtering backend.
- Documentation improvements.

-----
2019-08-30

- Added more filter lookups.
- Fixes in filtering backend.
- Improved test coverage for the filtering backend.
- Documentation improvements.

-----
2019-08-30

- Implemented custom lookups in favour of a single ``lookup`` attribute.
- Updated tests.