Version 16.3.1

Fixed

• Corrected a regression in which information sets were prematurely invalidated (and therefore
  delete this called on them) when removing the last node from an information set.
• Game.copy_tree and Game.move_tree implementations reversed the roles of the
  src and dest nodes (#499)

Changed

• For graphical interface, added support for wxWidgets 3.3; require minimum of wxWidgets 3.2.