Well… all the tests except the Peter Ellis Jones tests.
Pass around whole EnPassant types instead of pulling out just the e.p. square.
Make sure that Castling moves have their target and origin squares populated.
Add a color field to the Castle move style to make this possible.
Add an origin square argument to its one method ::ray_to_square(). Pushing this
implementation down a layer means I don't have to care about the color of the
piece.
This trait declares ray_to_square() which should return a BitBoard representing
a ray from a Square to another Square. The ray should include the target Square.
PlacedPiece implements this trait.
