Adding Vim Support

[roudy16]

Would you be interested in adding Vim support similar in UX to how Compiler Explorer does? I see some info regarding adding that functionality on the CodeMirror site here.

[roudy16]

I've added this feature locally, it is a pretty small change to leverage the vim extension for CodeMirror. @dunnoconnor, let me know if you want it, I can open a PR.