Now with events

This adds events as an example of how to avoid callback hell.

Some things:
* The observation of / emission of events is a NodeJS built in
* `util.inherits` is a quick way to prototypically inherit one JS class to another

![cow-barbecue](https://cloud.githubusercontent.com/assets/50366/3621172/c9e98b54-0e0f-11e4-8e81-f888e84770b6.jpg)