Add Castling

[puyanwei]

Castling is where the King and Swap positions with a Rook.

The following criteria must be forfilled for castling to be allowed;

• The King and Rook must not have moved previously
• The King cannot castle after its been in check
• There cannot be any pieces between the King and the Rook

Castling can also be applied left and right, and will move the King to the Knight's square and the Rook moves to the Bishop's square