Make setup.py Python 3 compatible
Remove tox.ini

Testing across Python 2.6 and 2.7 with tox is no longer working on systems
which doesn't ship both Python versions by default. I can install Python 2.6 on
a newer Ubuntu system using the deadsnakes PPA, but dependencies installed from
APT, like gobject and gstreamer are still only installed for Python 2.7, thus
making tox useless.