feature requests: callbacks on event

[matt-callanan]

Requesting callbacks on events, per our quick email exchange.

Here's how it works in node:

Client:

socket.emit('test', { an: "object", from: "the client" }, function(response) {
//do stuff with response, which == { an: "object", from: "the server" }
});

Server:

socket.on('test', function(message, callback) {
//do stuff with message, which == { an: "object", from: "the client" }
callback({ an: "object", from: "the server" });
});

[simb]

this was added via bwillard in a recent addition.