Merged PR #56.
Summary of code changes (in code order):
* Removed apply() in favor of inlined anonymous functions
* Removed ngModel.$render
* Added scope.$watch for attrs.ngModel
* Added callbacks.activate to store elements of ngRepeat and positions
* Added callbacks.receive to record a receive
* Minor changes to callbacks.stop that now utilizes values saved earlier
* Major changes to callbacks.update
* Minor changes to scope.$watch(attrs.uiSortable), (can be backported)