Implement iterable instantiation

[jay-tyler]

Want to instantiate PriorityQ with an iterable filled with val, priority iterables.

e.g.

PriorityQ[(1,3), (2, 4), ((4,3,4), 0), [[1,2,3,4], 5]) 

where each internal container is val, priority

We will also support using QNode as a flat level instantiator
e.g.

 PriorityQ[QNode(1,2), (3,4) (4,3), QNode(2,1)]

Internally, implementation will follow this provisional order (any changes to this will be advertised here):

1. examine the incoming items in iterable
2. if QNode, assign order and push to heap
3. if not, introspect item
4. if conforms to our proposed API: (val, priority):
5. init QNode with that priority, assign order, and push to heap
6. If no priority is supplied:
7. init QNode without priority, assign order, and push to heap

[jonathanstallings]

Thanks for setting this up. And for including our notes so that we can refer back if needed!

[jay-tyler]

Addressed here