MAKEDEV.8 improvement pack:
- 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.

Introduce MAKEDEV.man*, an equivalent of MAKEDEV.mi and MAKEDEV.sub
designed to output mdoc rather than shell script, and use them to produce
much better MAKEDEV.8 manual pages.

Note that MAKEDEV.man relies upon BSD m4 behaviour, which all m4 binaries
might not follow.

mdoc help and comments jmc@, disabused ok deraadt@