Rehearsal mark below/between staves

[Dave LaDelfa]

Spent a bunch of time trying to figure out how to do this, and failed. I'm going
to propose it as a feature request, unless someone goes "it already does that--
here's how."

The docs say (8.1.3) "\mark is only typeset above the top stave of the score." I
can think of a couple instances where this would be better off being adjustable:

1. Sometimes (typically in parts) text needs to attach to the rightmost barline
and be underneath the staff, i.e. the second example on doc page 8.1.3 -- I'd
like to have something like "D.S. as Fine" (say, "Minuetto da capo") go under
the staff, not over it.

2. Sometimes in an orchestral or band score it is helpful to the conductor to
see rehearsal letters in more than one place, e.g. top of the page, between the
winds and percussion, between the percussion and strings, and beneath the
strings. There ought to be a way to indicate (at score level?) by staff whether
to show the rehearsal letters above/beneath/both/not at all.

Dave LaDelfa