tour_rand1:    Brute force, go through all permutations.
tour_rand2:    Build path length as we go along.
tour_rand3:    Prune when path length >= best tour.
tour_rand4:    Use cheapest edges to obtain a lower bound.
tour_rand8:    Use min spanning tree for a lower bound.
tour_rand9:    Initialize with nearest-neighbor tour.
tour_rand10:   Initialize with two-opt tour.
tour_rand11:   Simple hash table.
tour_rand15no: Better hash table.
tour_rand15:   Only need tours w/ city 0 before city 1.
tour_solve -1: Assignment costs.
tour_solve -2: 2-factor costs.
tour_solve -H: Held-Karp costs.
tour_solve -HB1.001: guess bestlen <- 1.001*lowerbound.
tour_solve -Hk: Lin-Kernighan as initial tour.