Embolden each class of unimplemented feature.
Repeat the new tag line at the bottom of the readme.
Inlining ->combinators into make-rule doesn't make it any longer or
more complicated.

Looks like that change of interface, that we wrote way back when to
implement this program, was not actually necessary.
So, I don't actually need the system handler to look like a combinator
-- it suffices for it to look like a success continuation.  This
obviates all the activity with success objects in
user-handler->system-handler.
More accurate comment.
Much better nomenclature.
Clearer commentary.
Merge support/utils.scm into rules.scm since that's where those
procedures are used (and rules.scm is pretty small now).
A history section.
More accurate tag line and copyright statement.
Still more accuracy in tag lines.
Normally I hate writing "related work" sections.