[tor-dev] txtorcon suports "tor:" endpoint

I (finally!) merged David Stainton's "tor:" endpoint parser to txtorcon's master. This means two things: txtorcon now depends on txsocksx and you can do "client-type" things directly with endpoints, such as connecting to txtorcon's homepage:

ep = clientFromString("tor:timaq4ygg2iegci7.onion:80") ep.connect(...)

If anyone has strong feelings about txsocksx, I could be convinced to make the dependency optional (so you'd only get the "tor:" endpoint parser etc. if you happened to have installed txsocksx). Let me know!

Note that the last released version of txsocksx doesn't work with Twisted 15.0.0+ but there is a fix on master which does...