* Adds test/helper.rb and moves mock_app and other code specific
to testing the framework out of Sinatra::Test.
* Do not require test/unit. The sinatra/test/unit,
sinatra/test/spec, and sinatra/test/rspec files can be used to
choose the framework.
* Add Sinatra::TestHarness, which should act similar to the
Rack::Session proposal here: http://gist.github.com/41270
* Update the README with information on using the different test
frameworks.