Documentation generation issues in Python 3

[humanoid-path-planner]

Documentation generation issues in Python 3

[nim65s]

I also plan to add lxml to the dependencies in robotpkg, to get all the generated documentation.

[nim65s]

Also on this topic, @MaximilienNaveau pinged us with https://github.com/machines-in-motion/tuto_sphinx_doxygen

I think his goal is to generate a sphinx documentation website from the C++ docstrings, while the goal of doc/python/doxygen_xml_parser.py is to embed the C++ docstrings into the __doc__ attributes of the generated python bindings, but it might be worth taking a look at the tools used on both side.

[jmirabel]

I add the issue yesterday: e2814e5

[nim65s]

This looks better than my solution, thanks. Can we add this in devel ?