Resolve problem #24, and introduce framework conversion data changes

Resolve problem #24, and introduce framework conversion data changes

This introduces the conv_state schema, where state is saved
that records "automatic" changes the conversion makes to the
converted data.  When the MS Access data is changed and
the conversion re-run, the "new" automatic changes can be compared
to the changes made to the previous data set.

The "compare-state" make target can be used to report differences
between the old and new data.  Review this report to ensure
that the automated "fixes" do not change something that should
not be changed.