Investigate if STUN over TCP/TLS is beneficial to us

From client README:

-ice is a comma-separated list of ICE servers. These can be STUN or TURN servers.

This is not true, as right now only STUN over UDP is supported. We don't support any TURN servers, nor STUN over TLS (TCP).

We should clarify this in README, or implement support for those that are missing.

The STUN RFC contains a list of attacks that can be mitigated by STUN over TLS. I'm not sure if these are relevant for Tor's usecase.