run an eventmachine tcp server and handle callbacks

There are a few instances in which I've been polling when a callback would be a much better solution. I've added `Rubot::CallbackHandler` into rubot which uses a global variable to send a message to the specified channels. The callback format is simple:

```json
{
  "channels": ["#list", "#of", "#channels"],
  "message": "the message to send to the channels."
}
```