convert to minitest

[tenderlove]

Hi,

I hate changing other people's build tools, but test/unit is a thorn in my side while working on this code. I'd prefer if it was using minitest. That said, if you're tied to test/unit that's fine.

Thanks!

[mperham]

You need more pride in your changes, Aaron.

[westonplatter]

@tenderlove Sorry for the wait. I must have github issue notifications rigged to a gmail spam folder.

I don't have strong preferences, especially when there's just a handful of tests.

Merging.