Implement e.p. capture

Implement e.p. capture

For Chess and Mighty Lion e.p. capture was needed. This is controlled by
chessFlag, which also controlled the possibility to double-push M moves.
The e.p. captures are generated as two-leg moves over the victim Pawn,
after all other captures have been generated, and depending on promoSuppress,
which flags double-pushes, and is not used for other purposes in Chess
(where deferral is not possible, with Pawns promoting on last rank only).
When parsing input moves, e.p. capture is recognized, and expanded to
a two-leg move before searching it in the move list.