Django-weasyprint

- 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

- fix usage of urlparse in django_weasyprint.utils.django_url_fetcher

- added get_url_fetcher() method to allow easy override of the url-fetcher (Schnouki)