Noise protocol support

[tg-x]

Add Noise protocol support alongside TLS, now that an ocaml-noise library is available.

[samoht]

Patches are welcome :-) /cc @emillon and @talex5

[emillon]

I'm not very familiar with capnproto, but before doing that we'll probably need an implementation of NoiseSocket which is comparable to TLS (Noise only deals with what happens after the negociation is done and once the data sits in application buffers).