Add “Run” button to execute examples on jqplay.org

See https://github.com/jingweno/jqplay/issues/17 for more details. /cc @nicowilliams 

**Added button to run live examples**:

![screen shot 2014-09-08 at 10 36 19 pm](https://cloud.githubusercontent.com/assets/169064/4197103/433d1faa-37e3-11e4-8050-1ef1f6967188.png)

**Clicking "Run" to execute a live example**:

![screen shot 2014-09-08 at 10 36 55 pm](https://cloud.githubusercontent.com/assets/169064/4197119/74e1dcbc-37e3-11e4-881e-ab29e9fd096b.png)