python-chess v0.18.2

Bugfixes:

* Fixed castling in atomic chess when there is a rank attack.
* The halfmove clock in Crazyhouse is no longer incremented unconditionally.
  `CrazyhouseBoard.is_zeroing(move)` now considers pawn moves and captures as
  zeroing. Added `Board.is_irreversible(move)` that can be used instead.
* Fixed an inconsistency where the `chess.pgn` tokenizer accepts long algebraic
  notation but `Board.parse_san()` did not.

Changes:

* Added more NAG constants in `chess.pgn`.