Rails 4 support
* Update the spec/dummy app to use Rails 4 style
* Update the appraisals to use latest released rails versions
* Update travis config to pay attention to ruby 2.0 and rails 4.0
Use Bundler gem conventions.
use appraisal to test 3.1.0 and 3.0.10
test coverage for body_class method
use rspec for tests