added: onClose method parameter to notify() constructor

 * added: onClose method on notify() constructor
 * updated demo with:
```javascript
notify({
  messageTemplate: messageTemplate,
  classes: $scope.classes,
  scope:$scope,
  templateUrl: $scope.template,
  onClose: function () {
    console.log('closed at', new Date());
  }
});
```
 * updated version to 2.0.3
 * updated README.md