Allow to join several rooms at once

[darrachequesne]

The kind of change this PR does introduce

• a new feature

New behaviour

Enable the following:
socket.join(['room1', 'room2']);

Closes #2466, closes #2877

[NguyenTungs]

@darrachequesne
Thanks a lot. So great feature that.

[NguyenTungs]

@darrachequesne .
I've tried, and upgrade version 1.7.3

    "socket.io": "^1.7.3",

But that feature still not working.

Code here:

    socket.join(['tungns1', 'tungns2', 'tungns3']); // client join

But i changed :

   for(var i = 1, length1 = 4; i < length1; i++){
             console.log('tungns'+i);
             socket.join('tungns'+i);
    }

Then working.
So Could you review again that feature? Thanks a lot.

[darrachequesne]

Yep, it's not released yet.

[angel1st]

@darrachequesne - since we have now ability to join multiple rooms at once, shouldn't be nice to have the same for sending a message to multiple rooms?
I know, I can manage this like that:

['room1', 'room2', 'room3'].forEach(room => {
  // send message to all clients in the room, but the sender
  socket.broadcast.to(room).emit('message', 'nice game');
});

but I guess something like:

socket.broadcast.to(['room1', 'room2', 'room3']).emit('message', 'nice game');

will be more handy.

[darrachequesne]

@angel1st great idea! Could you please open a PR for that?