Add popover directive

Hello, I've built the popover directive for my use.  I've never done a pull request or anything so excuse me.  The tests are written and pass, demo is set up.  Maybe someone else can get some use out of it...

![popover](https://f.cloud.github.com/assets/454748/114629/0cc6b3e2-6bab-11e2-96f2-d2446b09fb49.png)

- Mike