splitting dl

[Jeff Kingston]

I'm also coming to the conclusion that splitting dl is the way to go.
We could use a whole new lot of files and keep the old ones, so that
old code would not break.  I did this when replacing @Fig by @Diag 
recently.
 
I'm not quite sure that I could label things "low-level" or "high-level"
as easily as Uwe seems to do.  I prefer to think of functionally
distinct parts of the system, such as "Fundamental Quantities" (initial
font and break, display gap, etc.), "Page Layout", "Displays and Lists",
"Large-scale structure" and so on.

If I undertook such a re-organization I would also want to look again
at the way format options work.  I think there needs to be a lot more,
and a lot more flexible, format options.  In fact I would go so far as
to say that all, or virtually all, format information should be in the
default values of format parameters, not hard-wired into the body of
the software at all.

Jeff