TODO

   1 allow markers on board for diagrams (add d_pieces to base_rules.js --> all the same purple circle)
   2
   3 add variants :
   4 Dark Racing Kings ? Checkered-Teleport ?
   5
   6 Hmm... non ? -->
   7 Otage, Emergo, Pacosako : fonction "buildPiece(arg1, arg2)" returns HTML element with 2 SVG or SVG + number