HTTP/SOCKS proxy support added (resolves DTVD/rainbowstream#60)

It's possible to use rainbowstream over a proxy without an updated PTT. PySocks (check https://github.com/Anorov/PySocks for more info) can be used to monkeypatch standard socket libs. So I gave it a shot and added HTTP/SOCKS proxy support.
Yes you're right, that should be 'SOCKS5'!