Remove unnecessary method getBoardHalf()
Refactor getPos() to pos()
Refactor gitRank() to rank()
Refactor getFile() to file()
Refactor getColor() to color()
Refactor getType() to type()
Refactor getMediator() to mediator()
Refactor get('mediator') to mediator()
Associate subscribers' CIDs with callbacks
Implement method unsubscribe()
Trigger at 'terminate' Square#resetPiece()
Allow pieces to unsubscribe
Implement limited en-passant capability
Remove unnecessary enPassantHandler()
Fully implement capturing en passant
Merge branch '26-12-pawn-queening-and-en-passant'