Django-weasyprint

- Pin WeasyPrint<53 due to module path change

- Handle `SCRIPT_NAME` being added to `MEDIA_URL` in Django 3.1
(https://code.djangoproject.com/ticket/25598)

- 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 empty `MEDIA_URL` (fd3fb30, 34)
- Add tests for views and `django_url_fetcher` & tox configuration

- Update signature of `weasyprint.default_url_fetcher` by Vlastimil Zíma (c9abfe8)
- Add `font_config` to handle `font-config` rules

An additional argument called font_config must be provided to handle
`font-config` rules. The same `fonts.FontConfiguration` object must be
used for different CSS objects applied to the same document.

https://weasyprint.readthedocs.io/en/latest/api.html#weasyprint.CSS