- Make get_left_bottom_right_top() const
  which means making some variables mutable so that update() becomes "const"
- Check if the lengthy name problem is still an issue
- Do we also want to offer functions left(), right(), top(), bottom() ???
- Find a better name for method get_bounding_box.
- Shall we store the iso-rectangle passed in the constructor
  in order to return the one that was passed to the constructor
  instead of a new one