Investigate Stockfish integration

[nelson137]

Add a way to play against Stockfish.

Investigate the position command:

• Do we need to send the full move list each time? position startpos moves <MOVES...>
• Can we just send a FEN? position fen <FEN> [moves]
  • The UCI docs seem to indicate that moves is required for the command

Stockfish communication

UCI documentation

Python implementation:

• Docs
• Source

[nelson137]

• Build script downloads Stockfish source code and compiles it
• Stockfish executable is embedded in the game executable
• On launch, the game installs Stockfish in <OS local config dir>/gambit/ if it doesn't already exist
• Implement communication with Stockfish process that is easily extensible
• For now, Stockfish plays as black