Implement UCI protocol

[tom-sherman]

https://en.m.wikipedia.org/wiki/Universal_Chess_Interface

https://www.shredderchess.com/download.html

As this is crate is no_std, the first step would be to implement a message parser and state machine with an API to send commands to the engine. This API can then be used to wire up to stdin/stdout for chess GUIs for example.

[tom-sherman]

I've whipped up a potential state diagram for the ICU engine, transitions are denoted with gui=* when they are transitions that are to be made on receipt of a command and engine=* for commands to be sent by us to the GUI as a side effect of a transition:

mermaid.js src

stateDiagram-v2
    [*] --> Ready: gui=uci
    Ready --> Identifying: engine=id
    note right of Ready
        Identify itself with the engine name,
        author, and options. Finally sending the
        uciok command.
    end note
    Identifying --> Idle
    Idle-->[*]: gui=quit
    # Idle --> Idle: gui=debug
    Idle --> Syncing: gui=isready
    Idle --> Configuring: gui=setoption
    Configuring --> Configuring: gui=setoption
    Configuring --> Syncing
    Syncing --> Idle: engine=readyok
    Idle-->Playing: gui=ucinewgame
    Idle-->Playing: gui=position
    Playing-->Playing: gui=position
    Playing-->Searching: gui=go
    Searching-->Playing: gui=stop
    Searching-->Playing: engine=bestmove

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[tom-sherman]

Thinking a little more, ICU might be more of a frontend (like web or terminal), than something that's built into the engine itself.