Some python3 updates.
Make sure we feed bytes to struct.pack/unpack for python3 compat.
Add dep on "six".
Bytes everywhere...

At this point, the test suites here pass on py2.6, py2.7, and py3.3.

Furthermore, my integration tests from another project pass with the
python-websocket-client library.
Merge pull request #23 from ralphbean/master

Python3 compatibility.