a few minor tweaks

Hi Gustavo,

I took a read through the code and added a few comments along the way.

There are still some things I don't understand, mostly the GitHub stuff in `hackedRefs` and what the `git-upload-pack` SubPath is about.

Nathan.
// Version represents a version number.

It doesn't really have to follow semantic version numbering, although that might be a good idea. Just following the idea of a major version that remains compatible is the only thing we need for gopkg.in to work.