Using the Sutherland-Hodgman algorithms convex and concave subject polygons can be clipped
by convex clip polygons.
For now we only need clipping to rectangles (Box), so limit our implementation to that. If needed this can be
trivially extended to convex clip polygons (a check whether the clip polygon is actually convex has to be added).
If convex clip polygons are needed we have to switch to e.g the Vatti algorithm.
Peter Keresztes Schmidt