WIP: Add pretty commit msg

As promised. It's dirty and it does not look *that* nice in source code, but it works:

![pretty_commits](https://cloud.githubusercontent.com/assets/5219415/3131360/a657bb84-e803-11e3-94be-2d80d255d6a8.png)

I think we might have to take care of the rare case that a file with `->` in its name gets renamed, but that's something we can deal with later.

Todo:
- [x] Use the editor that is created for the new file to insert the snippet instead of using the active one.
- [ ] Add specs.