Eliminating BitVectors

Debugged the new representation cutting the runtime on Block 10, v12 from 2:18 to 0:59.
Next commit will consolidate ngstate.py into gstate.py.

BTW, fringe_search works but is not faster on the Block 10 puzzle.  Perhaps when the search
space gets much larger (i.e., Climb-12 and beyond), fringe_search may pay off.