[noise] New draft with 0-RTT protocols

[Trevor Perrin]

Added clarifications from Jason:

https://github.com/trevp/noise/blob/master/noise.md


Also added a clearer set of 0-RTT protocols, which assume
pre-knowledge of a server ephemeral (or the server static) to send
encrypted data in the first message.

So this gives 18 handshakes:
 3x client static key is (none, known to server, sent to server)
 3x server static key is (none, known to client, sent to client
 2x 0-RTT variant

I think this is good, but I'd appreciate review.

Trevor