Implement LionChess

Implement LionChess

Add legality testing for Lions, so it ca be played with legality testing on.
Cyan markers are now also used in autonomous highlighting, so that double-
moving is triggered: A new move type FirstLeg instructs the marker callback
to use cyan on Lion contact captures. Igui required a special test, to make
XBoard realize the fial square is empty. Implement Lion-capture rules.
Forbid Pawn promotion to Lion: The Lion is skipped during the promotion
sweep (and it was not in the promotion popp anyway). Chu should not suffer
from this, as the piece used as promoted Kylin is not a real Lion (although
it looks like one). King is not considered a protector in Mighty-Lion Chess
This rule was added to allow trading Lions in the late end-game,
to prevent the game from being too drawish.