After enhancing namedtuple and ConfigParser, I found a simpler approach
that doesn't involve extending the API.  The simple way is to use
ordered dictionaries directly.  

With a small tweak to OD's repr, it is fully substitutable for a dict
without changing any client code or doctests (the OD loses its own
eval/repr order-preserving roundtrip but what json already gives now).

See attached patch.