1.4.3

• Separated the ideas of 'castling piece' and 'royal piece'. PieceType now has a castling field which determines whether a piece can castle. By default this is equal to royal, so most users don't need to worry about it - this is backwards compatible.
• The non-royal king in Kinglet chess can now castle.
• Variant: Extinction (MiscVariants.extinction()): game ends when a player doesn't have at least one of each piece type.