Notes on unifing DESCRIBE, INSPECT, and TTY-INSPECT

DESCRIBE, INSPECT, and TTY-INSPECT all do similar things.  Specifically,
they display internal information about an object, and allow the guts of it
to be examinded.

Given the similarity of what these three functions do, it would be nice to
only incode the knowledge about how objects are represented and what
internal information they have in one place.

This common code needs to examine the object, extract all the
sub-components, and (optionally) specify how to change the values of these
components.

X3J13 has specified that DESCRIBE works by calling DESCRIBE-OBJECT.
User supplied DESCRIBE-OBJECT methods are supposed to call DESCRIBE on
their components.  Therefore, the nature of recursing is specified for us.

But it does leave us lots of freedom.  Specifically, nested calls to
DESCRIBE can just emit some annotation that the supplied argument goes at
this place in the output, and arrange for DESCRIBE-OBJECT to be called
later.

But whatever we do, we want the naive usage of DESCRIBE/DESCRIBE-OBJECT
work reasonably.