v1.8

Pondering is now supported (go ponder, ponderhit, and the Ponder option).

• After go ponder the move to ponder on is entered and Psion searches as for go infinite; after ponderhit the time for the move counts from then on, while Psion goes on with its search. bestmove names the move to ponder on: the second move of Psion's principal variation (none after a book move or a move found at once).
• After stop (the opponent played another move) the adapter takes back the move pondered on and Psion's reply. Takebacks are now pressed at once and the position they lead to is accepted as soon as it is in memory, so this costs about 0.05 seconds of the engine's clock. Takebacks are also made when Psion considers the game over (e.g. after a mate it played while pondering), instead of replaying the game in a new game.
• A stop that arrives before the search has started (while the position is still being set up) is now answered with bestmove too.
• Pondering against not pondering: +70 ± 56 Elo in 100 games at 30+0.3 (self-play through python-chess, which sends ponderhit as lichess-bot does). While pondering, the engine uses a CPU core all the time.
• tools/lichess_check.py has a --ponder option.
• CI now runs the UCI integration tests on Linux and on Windows, with Psion Chess downloaded from Classic DOS Games, which data/README.md now points to.
• The README has a screenshot of Psion Chess.

Full Changelog: v1.7...v1.8