Proxy support

[anpic]

Can you add HTTP and SOCKS proxy support?
Maybe via the api from golang.org/x/net/proxy
https://github.com/jackpal/Taipei-Torrent/blob/6808fdfe24b4db505476ef48b9e288a5e7398f77/main.go#L107C6-L107C21
And it's better to make it possible to pass your own dialer creation function or dialer altogether.