Overlapping not adjusted

[MysticJay]

The Pan-Buttons move the map too far in one orientation and too short in the other orientation.
An item just off the screen does not show up after the pan.
The behavior is reproducible on the test; https://kartena.github.io/Leaflet.Pancontrol/
To reproduce: just move "Stockholm" off the upper edge, then pan.
Expected: "Stockholm" should show up inside the frame close to the other edge.

IMHO: an overlapping parameter should be added to allow a value between 0 and 50% of the view's width/hight.