pull out workflowop merge as ++ operator
experiment with test of WorkflowOp-level merging
respond to PR feedback
- don't use ++ since result is a weird tuple
- remove confusing comment
- make introduced names private in each class
- move rewrite method with fancy signature to the companion obj
Merge pull request #353 from mossprescott/ready/workflowop-test

Pull out WorkflowOp merging as a separate operator