Rust pop-answer: efficacy of trade-paths.

This answers the Rust pop-quiz to walk trade-paths and find advantageous trades.

The weighted path files, e.g.: kuji-depth-2.csv, are stored as CSV here.

The path-walker, ./efficacy, is here.

You see various path explorations.

Note that kuji-depth-4.csv has some paths that gain 10%+ in the chained trades.