Merge pull request #446 from karyon/py3prep

Py3prep & cleanup & a fix
moved to xlwt-future dependency
py3: tell travis we're using python 3.4 now. remove pypy, it doesn't support python 3.
make vagrant setup py3 ready
changes by 2to3
remove a encoding related hack that's not necessary with python3
rename all __unicode__ methods to __str__
use python3 super calls