Implement recursive lookahead.

refs #11
Fix debug prints.
Merge branch 'master' of github.com:osurdml/treemower into feature/11_implement_costmap_undo
refs #11 Implement part of undo/step functionality.
Merge branch 'master' into feature/11_implement_costmap_undo
refs #11 Step costmap for each descendant, not each group of descendants.
refs #11 Lawnmower works!
refs #11 Disable some debug messages.