add cleaning
workaround for sphinx assertion error

We were hitting sphinx bug documented at
https://bitbucket.org/birkenfeld/sphinx/issue/1160

This workaround makes those assertion error dissapear and
sphinx to finish happily.
fix sphinx errors&warnings; some pep8
add docs/_build to gitignore
Merge branch 'bug/fix-sphinx-build' into debian
add documentation package
remove docs/_static folder.

It was giving troubles with debian dh_sphinxdoc, due
to an old, unrecognized version of jquery being there that
could not be symlinked to the js-sphinxdoc version.
Merge branch 'bug/fix-sphinx-build' into debian
add python3 package