[doc] Do not rely on lgc's sphinx_ext This module is broken (getting an ImportError) and I don't want to fix it. The only usage we make of it is for the "autodocstring" directive, and I don't know what it does. Based on the context, replacing autodocstring with either automodule or autoclass and removing sphinx_ext from required Sphinx extensions.

version=3
opts=uversionmangle=s/(rc|a|b|c)/~$1/ \
https://pypi.debian.net/cubicweb/cubicweb-(.+)\.(?:zip|tgz|tbz|txz|(?:tar\.(?:gz|bz2|xz)))