This C extension implements a priority-queue object using a fibonacci
heap as the underlying data structure. This data structure supports
the following operations with the given amortized time-complexity:
- insert: O(1)
- find-min: O(1)
- extract-min: O(lg N)
- decrease-key: O(1)
- increase-key: O(lg N) (== delete, insert)
- delete: O(lg N) (== decrease-key, extract-min)