xhtml2pdf/xhtml2pdf 0.2.4

Maintenance release with several changes

on GitHub

Update link_callback documentation.
Stylize code lines in documentation.
Fixed cgi escape util on setup version.
Add test to python 3.7 and 3.8.
Fixed width assignation on fragments.
Support urllib in python 3 and python 2.
Add em unit support.
Repair base64 unscaped string.
Fixed urlparse when urls has parameters.
Fixed i_rgbcolor support.