add sample usage of badges with UIButtons and UIBarButtonItems

Wonderful stuff. Thanks for open-sourcing.

I've attached a `pull-request` that I used to enhance the demo to show how to quickly use the badges with `UIButton`s or `UIBarButtonItem`s ... would you be open to accepting these changes?

It would have saved me 1 hour and 7 minutes to feel assured that it would simply work and start using your library ... and I imagine if we take that collectively for all the folks who get your code and use it, that would add up to a lot of hours :)

![ios simulator screen shot sep 11 2013 2 23 53 pm](https://f.cloud.github.com/assets/821963/1125850/f054bd94-1b18-11e3-94af-bda5c29cc610.png)