Move the small helper functions to util

Not really part of final interface.
maphash functions for model parameters serialization
Add drop-db-table-cascade
Interface tweak for create-db-sequence
create-db-schema is redundant

Use pomo:create-schema.  Furthermore, we're moving to a one schema
backend for simplicity.
Macroize the make query functions
*to-json* and *from-json* are interface specials
Document *query-functions*
Call make query functions on demand

This is the big change that means we need not 'bake' models anymore.
Document and augment model parameters/specials

This are bound at two key times: to create the backend and when make
query functions are called.
Use new ensure-model-query code in model interface
Meta model parameters on demand fucntion

We have a bootstrap problem with going to the DB to find our model
parameters.  This is how to fix it.
No need for *db-schema* and sequence

It's a "one schema only" backend now.  Simpler.
Clean up backend creation
Clean up model creation with model parameters

See how we bind the specials to the params?  Those *same* params will be
bound we the make query functions are called on demand.  That is how it
should be (of course) and was a big mess when everything was just a
special variable (public or otherwise).

The neat trick is the INSERT call at the botton of create-model.  We are
eating our own dog food by keeping model parameters in our own model
table!
Drop model and backend public functions

Protected by restart-case but I still live in fear of accidental
deletions...
Flush the prepared queries

It would be nice to flush these on the DB side as well
Bring package exports up to date with recent changes
tests now compile and run again
REAMDE changes for new interface