Improve chess game

[vinc]

• Add save command
• Add load command
• Add play command
• Improve perf command output
• Improve error output

[vinc]

The save format uses the standard Forsyth–Edwards Notation.

It would have been better to use the Portable Game Notation to save the history of the game but the chess engine requires std to load this format. I may modify the engine to use nom internally instead of regex to work with no_std at some point.

The perf chess command uses the same kind of output as the hex shell command.