Design and implement further pluggable transport extensions

Sponsor F deliverable 4 is about designing and implementing further pluggable transport extensions. The original deliverable text is: "further extensions as needed from the Tor perspective for pluggable transport (proposal 180) support."

Quoting Roger here for more background: "Basically, we should make sure Tor is ready for whatever people are going to try to do with pluggable transports. Make Tor implement the pluggable transport spec, and make sure the spec is what we thought it should be. And guess what people will want it to be in the future so we're ready for that. And if somebody tries to use it for some of that future stuff, make it work for that."

Note that there's an overlap between this deliverable and the sponsor G milestone in June 2012 where we promised to finish the coding on Tor, obfsproxy, BridgeDB et al. to make pluggable transports work with obfs2 as proof-of-concept transport. The current plan is to finish the Tor coding until March 15, 2012 for this deliverable and the coding on obfsproxy and BridgeDB until June 30, 2012 for the sponsor G deliverable (#4566 (closed), #4567 (moved), #4568 (moved)).

This ticket gets auto-assigned to George. Not sure if Nick should lead this deliverable, because George already leads all the other pluggable transport deliverables for sponsor G.