Prepend scheme and hostname to relative links

[vCra]

Currently, when generating a pdf from a html file, I have to prepend {{ request.scheme }}://{{ request.get_host }} inside of my html, so that wkhtmltopdf will be able to access. Before the html is sent off to wkhtmltopdf, it should be parsed to check if any relative links are present, and if so, change them so that they are absolute.