This should include adding FunctorKeys that map to meas_base Result objects, and adding support for field creation to FunctorKeys, so the code that knows about the name conventions for compound fields lives in one place.

After adding support for creating fields to FunctorKeys, we should use this functionality to simplify the pure-Python plugins in meas_base's plugins.py.

I suggest that we might (continue to...) do some of this work on an as-needed basis, but that we're never going to assign somebody to just sit down and complete this ticket. I'm therefore closing as “Won't Fix”. Jim, please reopen if you disagree with that.