Apply rotation transformation on marker drag.

[Andrew-SK]

Potential fix for issue #9

During marker drag events the _setPos method is bypassed in favour of
setting the marker._latlng property directly. In order to account for
this the rotation must be applied after the MarkerDrag._onDrag method.
This is called repeatedly during the movement.

[Andrew-SK]

I realised it might be simpler to call marker.update() on the drag event, i.e.:

L.Handler.MarkerDrag.include({
    _onDrag: function (e) {
        proto_onDrag.call(this, e);
        this._marker.update();
    }
}

Rather than moving code into the _applyRotation method. I don't know if this would have any adverse effects.

[bbecquet]

Hi @Andrew-SK. Thanks for this great fix!
If I'm not mistaken by the Leaflet Marker update workflow, the alternative solution would call _setPos twice, which would result in coordinates being uselessly reprojected. So I'll merge the PR as-is. BTW, it's more explicit about what it does, so I like it 🙂

[Andrew-SK]

No worries, happy to help! 🙂