PriorityQueue API

[gkz]

Not content with add, remove Can't use deleteMin or deleteMax since we don't know if it's the min or max Thought about deleteTop - however, delete returns a boolean of whether the item was in the collection - would this be confusing?

Also, the static functions newNaturalMin and newNaturalMax - should they be functions, or subclasses of PriorityQueue - what would be a better name?