Add python3

Got this back up and running after rebasing to master. Then did an interactive rebase to squash the commits together (except where I add coverage.xml to gitignore)

There are still two integration tests failing in py3 land. 

The problem is that pylint depends on logilab-astng>=0.24.3 which does not have full python3 support.

astng changed their project to asteroid which does have the support so I need to get pylint to play nice with that somehow.