Zach Hunter's exitless paths search

[pozorvlak]

Minor cleanup of Zach's code, and an attempt to make it faster and more memory-efficient using the bitsets library.

This produces the same output as Zach's version until the call to findbests, at which point it throws the following error:

 Traceback (most recent call last):
  File "./exitless_paths.py", line 178, in <module>
    get(Ts, moves, 13)
  File "./exitless_paths.py", line 85, in get
    findbests(done)
  File "./exitless_paths.py", line 93, in findbests
    best[cost] = max(best[cost], max(len(p) for p in done[end][cost]))
  File "./exitless_paths.py", line 93, in <genexpr>
    best[cost] = max(best[cost], max(len(p) for p in done[end][cost]))
TypeError: object of type 'int' has no len()