Not Python 3 compatible

`python3 setup.py install` runs okay, but importing gives an error:

```
>>> from netfilterqueue import NetfilterQueue
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ImportError: /usr/local/lib/python3.4/dist-packages/netfilterqueue.cpython-34m.so: undefined symbol: PyString_FromStringAndSize
```
