General cleanup and future proofing

I've cleaned up the code, made methods where methods should be, used .on() in places where shorthand methods were used, added commenting and improved readability. I've also made the plugin ready for publishing on the [jQuery Plugins directory](http://plugins.jquery.com/) (see ScrollIt.jquery.json). For more on publishing this to the jQuery plugin directory, visit [publishing your jQuery plugin](http://plugins.jquery.com/docs/publish/).