Add minitest development dependency

Previously left out on accident.
Ruby 1.8.7 support

1.8.7 support was requested, and since it was easy to get the tests
passing, the request was obliged. Ongoing support is not garunteed, but
will be done for as long as it remains this easy.
0.9.3 release

* Support 1.8.7 (tests pass). Ongoing support will depend on ease.