Add Go Support!

![gogogadget](https://f.cloud.github.com/assets/836375/2330625/eabb9044-a437-11e3-8720-b1618577ac42.gif)

This also cases off runner appropriately and provides an error message if selection mode or file mode aren't configured. Interpreters only for selection mode here folks, unless we create a temp file.

![gofuckyourself](https://f.cloud.github.com/assets/836375/2330633/2dfd13fa-a438-11e3-8ddd-9ea690ed3929.gif)