Update Python and Django versions (vstoykov#19)

- Use latest supported Python and Django versions and drop Python 2 support
- Remove some deprecation warnings
- Use GitHub Actions instead of TravisCI
- Support passing None to validate_file_infection (vstoykov#18)
- Bump version to 1.0.0

Version 0.4.0

Bump version to 0.3.3

Bump version (0.3.2)

Fix setup.py

- Set classifiers corectly
- Set download and Bug track URL

Add MANIFEST.in

Version 0.2.1

Version 0.2.0

Set version to 0.1.0