parameter substitution.
ok todd@

- refer to the section 4 manual page for every device target, whenever
possible
- repair a few minor quoting errors
- repair a few sorting errors
- fix a few device descriptions (ideally they would be synched with the
.Nd line of their manpages, but we are not there... yet)
- minor mdoc fixes
Thanks to jmc@ for review and a lot of constructive criticism.

While there, allow the comment char and the divert section for md script
fragments to be overriden.
No functional change (yet).
disabused ok deraadt@

'the big disk case' no longer sets vars and calls dodisk, would take more space
to additionally do the 'stepping' argument (see cd\* in generated MAKEDEV)

prepare dodisk* script functions for a 7th argument, what I call disk stepping,
the number to add from rd0a to rd1a minor numbers, defaulted to 16; some archs
*cough*macppc*cough* still have 8 for cdroms and such

.mi    -> edit this to add new devices
.sub   -> hardcore m4 here, be careful
*/*.md -> machine dependent information (generally device,block (& char) major)
Thanks for eyes/conversation about this over the years from espie, deraadt,
johns, fgsch, hugh, weingart, mickey, and others ..
SEE ALSO
.     m4(1), MAKEDEV(8)