Rust pop-answer: vern-prime

Rust pop-answer to generalizing ./vern to any paths, A -> B:

./vern, my main man, ./vern got a face-lift.

n.b.:

./vern n A data/market.lsv data/A.csv

For some token, A

is idempotent to

./efficacy n data/market.lsv data/A.csv