Django-weasyprint

- Pin WeasyPrint<53 due to module path change

https://github.com/fdemmer/django-weasyprint/blob/master/CHANGELOG.md#110---2021-02-19

https://github.com/fdemmer/django-weasyprint/blob/master/CHANGELOG.md#102---2020-10-07

- Fix classifiers and changelog

- Drop Python 2 support: WeasyPrint >= 43 and Django >= 2.2 are required

- Update README to demonstrate override of URL fetcher (65ced6f)
- Fix URL fetcher when used with emtpy MEDIA_URL (fd3fb30, 34)
- Add tests for views and django_url_fetcher & tox configuration