Add Python 3.4 to classifiers in setup.py.

I've ran the test suite with Python 3.4.0:

    $ python3.4 -m venv venv34
    $ . venv34/bin/activate
    $ pip install -e .
    $ cd tests/
    $ ./runtests.py
    ...
    Ran 6783 tests in 313.773s

    OK (skipped=540, expected failures=7)