Refactor Operations/AggregatorOperations for convenience in preparing to continue removing *args
Move remainder of operations from Assembly into Operations catch-all and refactor insert
Remvoe distinct; not sure why it was even there given that it raises immediately.  Should re-engineer wrapper around Unique AggregateBy instead.
Update debug pipe contract to match Cascading
Refactor and document ungroup/set_value/etc.; this is a non-backwards compatible change