chess-legal-plies: If chess-ply-allow-interactive-query is nil, generate Q and N promotions.
chess-ai.el: Quiescence search.

This change finally fixes the internal Emacs Lisp based AI enough
to be an interesting opponent.  Search is of course very slow, and
rather shallow (2 plies + quiescence by default) but the AI can finally
defend itself against simple attacks, and sees opportunities as expected.
chess-ai.el: Cleanup.
chess-ai.el: Rename functions and fix a subtle bug in quiescence search termination.
chess-ai.el: Better top-level move ordering and quiescence pruning.
chess-ai.el: Require cl-lib at runtime for cl-sort.
Build fruit and glaurung modules.
chess-ai.el: No need for cl-sort.
chess-ai.el: Oops, cl-delete-if only at runtime.