Go rewrite

Wanted to learn Go, so here we are.

This is probably a bad pull request, since it removes some features and doesn't add much to performance. On the other hand, no one cares about this repo so :notes: *I can do whatever I wanttttt* :musical_note:. All the performance hits are incurred through libgit2, so the Ruby and Go versions are more or less on par at the moment, though I have thoughts on that.

The output does look a little flashier now, though. Here's what we've got on our main GitHub repository at the moment, which takes about eight seconds or so to traverse the 200k commits:

![screen shot 2014-12-13 at 12 08 00 am](https://cloud.githubusercontent.com/assets/2723/5423095/21e22738-825c-11e4-9528-622994f8c69d.png)

I still need to figure out the binary situation, but that'll be cooler than demanding people install fucking Ruby.

Fixes #1.
We should move the creation (and compilation) of the regex object outside of the loop here. It only needs to be made and compiled once then only used to match inside the loop from then on. Basically, just move the `regexp.MustCompile` part above the loop then reuse that object inside to call `FindAllString`. It should help performance a bit too.