Support for Python 3 and UDP

[diogobaeder]

Hi!

These changes introduce support for Python 3, both for the client and for the server. Though I didn't end up creating any automated test for the server part (there's almost no test there, so I thought it would delay too much to start introducing them), I tested this manually, and it's working for both Python families.

Also, I'm introducing UDP as a graphite transport ("graphite-udp"), so that we're able to get the pystatsd server sending messages through UDP to carbon (for me, at least, this will be super useful!). This brings more coherence as well to the package as a whole, since we already send statsd messages through UDP.

For testing, I introduced tox, so that we can have the project build running under both Python families.

Please let me know what you think.

[diogobaeder]

Do you intend to maintain support for Python 2.6? If so, then I'll have to figure out a way to have it running here in my computer (I don't use 2.6 for a very long time) and test it, because in 2.7 all tests pass.