Django-webmention

Added
- Support for Django 4.0+

Removed
- Support for Django versions less than 2.2
- Support for Python versions less than 3.7

Fixed
- Store source content as a string rather than a bytes object

Fixed
- Render HTML links in the Django admin by using `format_html` instead of the now-deprecated `allow_tags` attribute

Removed
- Support for Python 3.5

Added
- Compatibility in the `include_webmention_information` decorator for versions of Django with new-style middleware

Changed
- Use static `setup.cfg` for package metadata and tooling configuration
- Use black code style
- Lint with pyflakes

Fixed
- Made `setup.py` aware that the README content type is, in fact, markdown