Add max-depth as parameter to search.

[TyOverby]

[radix]

To clarify, I hope this can be done as a maximum cost, not just maximum depth of nodes traversed. I am using astar for pathing in a square grid with realistic distances, i.e. diagonals are sqrt(2) apart whereas direct adjacency is only 1 apart, and I'd like to have a way to limit the maximum distance traveled in a path