Chess

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New features:

* Use ``chess.engine.Opponent`` to send opponent information to engines.
* Inform engines about the game result using
``chess.engine.Protocol.send_game_result()``.
* Add ``chess.engine.Limit.clock_id``.
* Add ``chess.svg.board(..., borders=True)``.
* Avoid rendering background behind SVG boards to better support transparency.
* Add ``chess.pgn.BaseVisitor.begin_parse_san()``.
* Introduce new distance metrics ``chess.square_manhattan_distance()`` and
``chess.square_knight_distance()``.

Bugfixes:

* Fix ``chess.pgn.GameNode.eval()`` sometimes off by one centipawn.
* Fix handling of additional spaces between UCI option tokens.
* Handle implicit XBoard engine resignation via output like
``0-1 {White resigns}``.

Changes:

* Add model ``sf16`` for ``chess.engine.Score.wdl()``, the new default.
* Update ``lichess`` WDL model.
* Keep PGN headers that do not belong to the Seven Tag Roster in insertion
order.
* Halve the number of open file descriptors maintained by tablebases
and opening books.
* Reduce verbosity of logged ``chess.pgn`` errors.

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Bugfixes:

* Fix ``PovScore.wdl()`` ignored ``model`` and ``ply`` parameters.
* ``chess.syzygy``: Check that board matches tablebase variant.

New features:

* Add model ``sf15.1`` for ``chess.engine.Score.wdl()``.
* Raise more specific exceptions: ``chess.IllegalMoveError``,
``chess.AmbiguousMoveError``, and ``chess.InvalidMoveError``.

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Bugfixes:

* Fix some valid characters were not accepted in PGN tag names.

Changes:

* Skip over syntactically invalid PGN tags.
* Detect Antichess insufficient material with two opposing knights.

New features:

* Add ``chess.Board.unicode(..., orientation=chess.WHITE)``.

-----------------------------

Bugfixes:

* Fix recursive Crazyhouse move generation sometimes failing with
with ``RuntimeError``.
* Fix rendering of black pawn SVG on dark background.

New features:

* Add ``chess.engine.AnalysisResult.would_block()``.

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Bugfixes:

* Reject pawn capture SAN if the original file is not specified, e.g.,
``d5`` will no longer match ``cxd5``.

Changes:

* Tweak handling of whitespace in PGN comments: When parsing, any leading
and trailing whitespace (beyond one space) is preserved. When joining
multiple PGN comments, they are now separated with a space instead of a
newline character. When removing annotations from comments, leftover
whitespace is avoided.

New features:

* Add model ``sf15`` for ``chess.engine.Score.wdl()``.

-----------------------------

Bugfixes:

* Expand position validation to detect check conflicting with en passant
square.

New features:

* Add ``chess.svg.board(..., fill=...)``.
* Let ``chess.svg.board()`` add ASCII board as description of SVG.
* Add hint when engine process dies due to illegal instruction.