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)
