Stick with MiniTest 4.

Make sure not to use MiniTest 5.x yet, because
Turn is not compatible with it. See:

    https://github.com/TwP/turn/issues/122
Remove version constraint on rake.
Use Ruby 2.0 with rbenv.
Add license property to gemspec.
Keep gems in .bundle instead of vendor/bundle.
Update gems.
Add encoding specification in pathname.rb.

Needed to interpret multibyte sequences correctly.
Update README.
Bump version number.
Add release notes.
Fix parsing of drush pm-releases.

Recent versions of drush have changed the output
of the pm-releases command. Fix the code
accordingly.
Add a test.
Add methods to inspect a version type.
Update README.
Document Version.<=>.
Add Version.better method.

This is meant to be used to determine the best
candidate for updating a project based on the
degree of stability.
Add tests for Version.better and Version.<=>.
Replace the logic for finding the best release.

Instead of relying on Drush's “recommended” and
“supported” release, use custom code to find the
“best” candidate for updating a project.
Refactor Project.fetch.
Fix parsing of Drush output by using YAML format.