Claim Python 3.4 compatibility

There's one deprecation warning that we should fix:

    .tox/py34/lib/python3.4/site-packages/zope/tal/htmltalparser.py:110: DeprecationWarning: The value of convert_charrefs will become True in 3.5. You are encouraged to set the value explicitly.
      HTMLParser.__init__(self)

The travis build is blocked on
https://github.com/travis-ci/travis-ci/issues/1989