Auto-join on socket.connect()

[phisad]

For single-player games it might be interesting to also provide an "auto-join" option.

Currently we need this:

socket.connect();
socket.emit("join", {"room_id": "compreg_room"});

Maybe something like this might be enough

socket.connect({"autojoin":"default_room"});

with server-side:

@socketio.on("connect")
def client_connect(auth, data):
    if "autojoin" in data:
       socketio.emit("join", {"room_id": data["autojoin"]});

If sufficient in most cases, this might become the default behavior.