get legal capturing moves.

returns `directionsToUse` and whether slot matches plr - if not wrong turn and wrong slot.

get legal *moving* moves.

returns a slot and its I (after calc).

NewBoard() returns an initialized board set-up for a checkers game.

TODO: actually make it so can play different size boards?.

an unoccupied dark square.

Not A Spot (a light square).

blue goes down.

red goes up.

Board is a 2-d arrays, that's represented in a 1-d array.