added: onClose method parameter to notify() constructor

[pedrombafonso]

• added: onClose method on notify() constructor
• updated demo with:

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