revamped gem for rails 4

hi, did not work for me using rails 4, so i revamped the gem to use latest jquery plugin. changed to !coffee javascript so the coffeescript gem is not required. fixed a couple of typos, too. now, it works fine for me. did not test using rails 4, so in ended up with ```gem.add_dependency "railties", "~> 4.0"``` for now. maybe adding a 'rails-4' branch might be a good thing for now to do. regards, tom