Implement move exclusion

Implement move exclusion

A 64KB moveMap[] is added to keep track of which moves are excluded in the
root. It is indexed directly by the lowest 16 bits of the move code,
(the from- and to-square), and can be almost entirely used, as the board
measures 121 squares, an the 'shadow' board (another 121 squares) can be used
both as from- and to-square as well. So that in theory 242*242 moves can
be encoded.