feat(connected-disconnected): add signals for connection state

This is a stopgap before a full event overhaul for a 4.x release
of this module. These event names will not change (thus do not
need a major push), but where they are emitted from might be
subject to change in the future

lib/amqp_client.js

@@ -120,6 +120,7 @@ AMQPClient.prototype.connect = function(url) {
 
       self._session.once(Session.Mapped, function(s) {
         debug('mapped');
+        self.emit('connected');
         resolve(self);
       });
 
@@ -128,6 +129,7 @@ AMQPClient.prototype.connect = function(url) {
 
     self._connection.on(Connection.Disconnected, function() {
       debug('disconnected');
+      self.emit('disconnected');
       self.emit(AMQPClient.ConnectionClosed);
       if (!self._shouldReconnect()) {
         self._clearConnectionState(false);
@@ -301,11 +303,13 @@ AMQPClient.prototype.disconnect = function() {
       self._clearConnectionState();
       connection.once(Connection.Disconnected, function() {
         debug('disconnected');
+        self.emit('disconnected');
         connection = undefined;
         resolve();
       });
       connection.close();
     } else {
+      self.emit('disconnected');
       resolve(); // Already disconnected, just deliver the promise.
     }
   });