Let's finish 8-puzzles and TSP (AIMA 3.22)

Some unfinished business from last week: Prasan's working on a definitive test of solvability; Glenn's possibly modifying his heap implementation to do rekeying. And then there's TSP.

See last week's meetup (https://www.meetup.com/LA-Computer-Science-Reading-Group/events/84102962/) for a description of 3.22.