WIP: EventEmitter Subscription

[rakyll]

Please don't merge.

Modifying Subscription to poll messages automatically.

var sub = conn.subscribe('sub1', { autoAck: true });
sub.on('ready', console.log);
sub.on('error', function(err) {
  console.log(err);
});
sub.on('message', function(message) {
  console.log(message);
});
sub.close();

[rakyll]

Benchmarks for 50 messages:

• 17512ms without auto-ack
• 32538ms with auto-ack

[rakyll]

b/16573214 and b/16571871 for latency issues.