Send unicast messages in background too

In general, protocol designs should not assume the underlying layer to
provide reliable transmission of a message or guaranteed receipt of
confirmation.  Application level protocols that wish to guarantee
delivery should implement its own acknowledgement mechanism.

Note that our consensus (modeled after PBFT) does not require such
positive acknowledgements of each message sent.

p2p/peer.go

@@ -31,7 +31,7 @@ func SendMessage(peer Peer, msg []byte) {
 	// Construct normal p2p message
 	content := ConstructP2pMessage(byte(0), msg)
 
-	send(peer.Ip, peer.Port, content)
+	go send(peer.Ip, peer.Port, content)
 }
 
 // BroadcastMessage sends the message to a list of peers