Examples for the different ways .on() can be used

Had a coworker that was confused about where to find documentation on the different ways `.on()` can be used. Turns out there's a single kinda throwaway sentence in the current docs for it, so I thought adding some examples would help.

![on-examples](https://cloud.githubusercontent.com/assets/49545/3930235/16b82e80-243c-11e4-9ca7-8a6297e8948a.PNG)