Don't re-export map or array

I anticipate having at least two flavors of maps and arrays (persistent
and declarative).  I can't anticipate which flavor the user will want so
make him ask for a flavor by name.
Non-working sketch of persistent map

The goal is to make a persistent map with a canonical structure and
declarative semantics.  I want map operations that I can run forwards
and backwards.

This code is pretty ugly and doesn't work.  I'm playing with what might
work and then refining towards a more declarative implementation.