Add support for Django3 and drop support for Python2

Updates for compatibility with Django3 and dropping support for Python2.

Updates for compatibility with Django3 and dropping support for Python2.

Fix deprecation warning, add py3.7 CI envs and black code formatting

v1.0.2

Bump version for release

Fix bug preventing use of multiple ConstantGroups

v1.0.1

Add extra CI envs and try codecov bash uploader

Initial release

v1.0.0

Update Codecov badge to hit Codecov directly