[qjcluonu] Crazyhouse immediate drop

Modify shogi or the chess variant crazyhouse so that captured pieces must be immediately dropped on the same move.

We could put restrictions on where a piece may be dropped, and if there is no place a captured piece may be dropped, then it may not be captured.  Could easily make colorbound pieces remain identically colorbound after being captured.

Abstractly, any move is a permutation of the pieces on the board (ignoring color); the number of pieces on the board remains constant.  Maybe start with a less dense board.