Add support for tox (http://tox.testrun.org/) and Travis CI (http://travis-ci.org/)

Sample Travis CI build: http://travis-ci.org/#!/msabramo/gevent-socketio/builds/1699184

Tox output:

```
[last: 4] marca@SCML-MarcA:~/dev/git-repos/gevent-socketio$ tox
GLOB sdist-make: /Users/marca/dev/git-repos/gevent-socketio/setup.py
py27 sdist-reinst: /Users/marca/dev/git-repos/gevent-socketio/.tox/dist/pysocketio-0.9.6a1.zip
py27 runtests: commands[0]
running test
running egg_info
writing requirements to pysocketio.egg-info/requires.txt
writing pysocketio.egg-info/PKG-INFO
writing top-level names to pysocketio.egg-info/top_level.txt
writing dependency_links to pysocketio.egg-info/dependency_links.txt
reading manifest file 'pysocketio.egg-info/SOURCES.txt'
reading manifest template 'MANIFEST.in'
writing manifest file 'pysocketio.egg-info/SOURCES.txt'
running build_ext
test_ack (socketio.tests.protocol.DecodeTest) ... ok
test_ack_with_args (socketio.tests.protocol.DecodeTest) ... ok
test_ack_with_bad_json (socketio.tests.protocol.DecodeTest) ... ok
test_connect (socketio.tests.protocol.DecodeTest) ... ok
test_connect_with_querystring (socketio.tests.protocol.DecodeTest) ... ok
test_decoding_newline (socketio.tests.protocol.DecodeTest) ... ok
test_disconnect (socketio.tests.protocol.DecodeTest) ... ok
test_error (socketio.tests.protocol.DecodeTest) ... ok
test_error_with_endpoint (socketio.tests.protocol.DecodeTest) ... ok
test_error_with_reason (socketio.tests.protocol.DecodeTest) ... ok
test_error_with_reason_and_advice (socketio.tests.protocol.DecodeTest) ... ok
test_event (socketio.tests.protocol.DecodeTest) ... ok
test_event_with_data (socketio.tests.protocol.DecodeTest) ... ok
test_heartbeat (socketio.tests.protocol.DecodeTest) ... ok
test_json (socketio.tests.protocol.DecodeTest) ... ok
test_json_with_message_id_and_ack (socketio.tests.protocol.DecodeTest) ... ok
test_message (socketio.tests.protocol.DecodeTest) ... ok
test_message_with_id_and_endpoint (socketio.tests.protocol.DecodeTest) ... ok
test_ack (socketio.tests.protocol.EncodeTest) ... ok
test_ack_with_args (socketio.tests.protocol.EncodeTest) ... ok
test_connect (socketio.tests.protocol.EncodeTest) ... ok
test_connect_with_querystring (socketio.tests.protocol.EncodeTest) ... ok
test_disconnect (socketio.tests.protocol.EncodeTest) ... ok
test_error (socketio.tests.protocol.EncodeTest) ... ok
test_error_with_endpoint (socketio.tests.protocol.EncodeTest) ... ok
test_error_with_reason (socketio.tests.protocol.EncodeTest) ... ok
test_error_with_reason_and_advice (socketio.tests.protocol.EncodeTest) ... ok
test_event (socketio.tests.protocol.EncodeTest) ... ok
test_event_with_data (socketio.tests.protocol.EncodeTest) ... ok
test_event_with_id_and_ack (socketio.tests.protocol.EncodeTest) ... ok
test_heartbeat (socketio.tests.protocol.EncodeTest) ... ok
test_json (socketio.tests.protocol.EncodeTest) ... ok
test_json_with_id_and_ack (socketio.tests.protocol.EncodeTest) ... ok
test_message (socketio.tests.protocol.EncodeTest) ... ok
test_message_with_id_and_endpoint (socketio.tests.protocol.EncodeTest) ... ok

----------------------------------------------------------------------
Ran 35 tests in 0.010s

OK
_________________________________________________________________________ summary __________________________________________________________________________
  py27: commands succeeded
  congratulations :)
```