and __setstate__() doesn't run if the state is False.

Ensure that we always return a non-false state (another version bump
here).

This adds a tool for computing the iname nest efficiently, for printing.

Closes #5

dependencies, and also to treat loops more carefully.

* Dependencies are now tracked based on a list of active potential
  sources, and the active set is narrowed by filtering through
  readers/writers
* Stricter handling of dependencies within loops by not assuming
  that loops are nonempty
* Changes the barrier insertion algorithm to act in two stages: first,
  barriers are recursively inserted into loops, then they are inserted
  at the outermost level. This is mostly meant to simplify the code.
* See also #18 on gitlab

check that the index returned is a minimum, rather than the exact value from numpy (in case of duplicate min/maxs)