Protochess engine

This is a fork of raytran/protochess with some major modifications.

• 100% user-defined pieces, instead of hardcoding the standard chess pieces.

• Add complex (slow) generation of piece-square tables and material values, since it greatly improves strength and it's only done once at the start.

• Full support for:

  • Standard chess
  • Chess960, Transcendental chess
  • Antichess / Giveaway / Losing chess
  • Atomic chess
  • Horde
  • Racing kings
  • Three-check, Five-check
  • King of the hill
  • Any custom variant that can be defined using the currently supported rules.

• Fixed some bugs in the original engine and added more tests.

• Faster move generation and more aggresive game tree pruning.

• Multithreading support, using the Lazy SMP algorithm with a lockless transposition table. (Use the parallel feature when compiling. For example: cargo build --release --features parallel)

• Better WASM support, using web workers to run the engine (with or without multithreading) without blocking the UI.