Remove Turn

The newest versions of MiniTest have much better output formatters than
they used to
Move minitest requirement into the rakefile

So that it doesn't get accidentally loaded twice when the rake default
test task hoovers up all the files in test/ when loading all it's files
MiniTest::Unit::TestCase is now MiniTest::Test

fix all the references from the old MiniTest::Unit::TestCase and the
even older Test::Unit::TestCase to the new MiniTest::Test