[noise] Go implementation

[Jason A. Donenfeld]

Please don't DoS my server or abuse this, but here's a stream of dmesg:

$ nc test.wireguard.io 42912

Running either of those programs should yield:

[122160.077355] wireguard: Receiving handshake initiation from peer 1
[122160.077367] wireguard: Sending handshake response to peer 1
[122160.084991] wireguard: New noise session created
[122160.110627] wireguard: Received keepalive packet from peer 1
[122160.120336] wireguard: Old noise session cleared and freed