[improvement] Add CenterMouseWhenMouseWheelZoom-ish property

[itschrono]

Hello,

I think that for the mouse wheel zoom options (MouseWheelZoomType). Only 2 would be enough:

• MousePosition
• ViewCenter And a new property CenterMouseWhenMouseWheelZoom (boolean) to decide wether or not it should center the mouse while zooming. Or a enum CenterMouseOption { CenterIfMousePositionZoom, CenterIfViewCenterZoom, NeverCenter } ? For my concern I want to use ViewCenter without the mouse to move, I think it's pretty annoying. Please give some heads up then I may do a pull request :)

[itschrono]

Easy bypass:

       internal void Init(GMapControl gMapControl)
        {
            var c = gMapControl;
            c.MouseWheel += GMap_MouseWheel;
            c.MouseWheelZoomEnabled = false;
        }
        private void GMap_MouseWheel(object sender, MouseWheelEventArgs e)
        {
            if (e.Delta < 0) GMapControl.Zoom--;
            else GMapControl.Zoom++;
            e.Handled = true;
        }