* Handle making a column NOT NULL with a Django default value as backward incompatible.
This should have been the case from the beginning, but it was not.
When one uses the `django-add-default-value` lib, the operation should still be compatible.
* Improve behaviour of the `--include-migrations-from` option.
When the given filename is missplelled, fail instead of linting all migrations.
When the file is empty, lint no migrations instead of linting all migrations.
* Update libraries used for testing (`tox`, `flake8`, etc.)