Simple binary heap implementation of priority queue

[cicirello]

Summary

The existing BinaryHeap class supports constant time containment checks which enables efficient priority changes and arbitrary removals. It accomplishes this by maintaining a hash table based index into the heap.

Additionally, the existing class limits use to distinct objects, related to hash table use.

Add a simpler binary heap class without the hash table based index. Some applications may not need containment checks, priority changes, and arbitrary removals. Provide alternative without the overhead associated with this. Also allow duplicates.