Added toString() for Sender.
Added string input to Sender constructor, to allow: socket.write(""+new Packetizer.Sender('You said \"'+msg+'"'));
Added Packetizer.send(<String>) function.
added receivePromise and testServerPromise.js to use it.
added rejection on 'error' in .receive (aka receivePromise).
added unit tests for .send and .receive