Connection as a Writable stream

[mcollina]

I moved the parsing logic directly inside the Connection object, which became a Writable.
It is not needed to be a Duplex, as it will do nothing in writing.

The interface remains the same, but it allows cool stuff like:

// stream is from somewhere, it might be a named pipe, a websocket, or whatever other transport

var mqtt = require("mqtt");
var conn = stream.pipe(new mqtt.Connection());

conn.publish("hello", "world");

Fixes #121

@adamvr and @timoxley please provide feedbacks :).

I'd like this to go into #118, as it simplifies the reconnecting logic.

I'd like to also expose this through the "main" mqtt object, so we can do "crazy" ideas like MQTT over Websocket (and any other kind of Stream).

[mcollina]

I'm also in favor of deprecating createConnection, createServer and createSecureServer.
All of these are just convenience methods around a Connection object, and to me they seem just to make things more complex.

[timoxley]

A big +1 from me for all of the above.

[timoxley]

Would #121 come back perhaps in a later version?

[adamvr]

👍 to connections as streams, duplex, writable or otherwise. Much more portable. As to the createX methods, what is your alternative @mcollina? Would we do something like:

var conn = new mqtt.Connection()
    , sock = net.connect(1883, 'localhost');

sock.pipe(conn);
conn.on('connect', ...)

That seems to me to be more complex, unless I'm missing something here.

[mcollina]

Ok, let's leave this reasonings to a next version and merge this.