TODO

   1 Full detection of repeated positions (including turn)
   2 In UltimaChess, consider these rules modifications: http://www.inference.org.uk/mackay/ultima/ultima.html
   3 Reintroduce isAttackedBy in Ultima, and fix it for pawns --> underCheck + stalemate
   4 --> take into account that an immobilized piece does not give check.
   5 (chameleons cannot be immobilized)