Add way to diff AnnotationViewPlus type

[ininex]

I don't really know how to check the type of my pin annotation type in delegate mapView(_ mapView: MapViewPlus, calloutViewFor annotationView: AnnotationViewPlus) -> CalloutViewPlus. The AnnotationViewPlus comes from nowhere, now define CalloutViewPlus is mandatory. What if I only want one pin to show callout view but not others? Having that hacking method to hide callout view for certain pins(as another issue thread mentioned) is kind of silly. Why don't you change this delegate return value as optional? I cannot show other subclass of MKAnnotation if I use only MapViewPlus, it just crashes as the mapView(_ mapView: MKMapView, viewFor annotation: MKAnnotation) -> MKAnnotationView? is overriden by MapViewPlus's delegate