Add directives for select2 custom events

[Soviut]

It would be worth-while having custom select2 event directives for select2 events such as select2-opening. I needed to create one of these for triggering an analytics event to detect opening, even if the user doesn't change the model.

The code is based heavily on angular's own event directives.

app.directive('select2Opening', function($parse, $rootScope) {
    return {
        restrict: 'A',
        compile: function($element, attr) {
            var fn = $parse(attr.select2Opening);
            return function(scope, element) {
                element.on('select2-opening', function(e) {
                    var callback = function() {
                        fn(scope, {$event: e});
                    };
                    scope.$apply(callback);
                });
            };
        }
    };
});