Yet another major update

1. Added onReady and onChange events for container.
2. jQuery plugin definition has been updated. It's now possible to
access methods via the plugin declaration. eg.
$(selector).cascadingDropdown('getValues') will return an object with
values from all dropdowns within scope.
3. Code cleanup. Probably needs a more thorough cleanup.
Updated version number

Version is now 1.2.0.