[Nmh-workers] argument splitting documentation

[Ken Hornstein]

I've finished the conversion of everything appropriate (I think) over to
the new argsplit code.  This lets people put things like:

moreproc: less -R

in their .mh_profile (or even on the command line with things like -moreproc).

But one thing comes to mind: where should this be documented?  In
mh-profile(5)?  Each command man page?  Somewhere else?

--Ken