landscape mode vs. new paper size

[Graham Percival]

Hi James,

I managed to add a [landscape] option to @lilypond, but it prints
music rotate 90 degrees.  In retrospect, that should have been
obvious -- that's exactly what we want landscape to do!  But it's
not useful for the NR 3 spacing chapter.

How about defining a spacing-doc (icky name) page size?  So that
NR 3 Spacing  can use:
  @lilypond[pagesize=spacing-doc]
(I'm not certain if hyphens are allowed in paper sizes)

which would have landscape dimensions, without being rotated?  We
could even add a series of doc page sizes (doc1, doc2, doc3...)
with different sizes... doc1 could be the smallest, and intended
for a tagline only; doc2 might be intended for two staves (to show
some staff-staff spacing stuff), while doc3 could be intended to
hold two piano staves, etc?

Think about it, and maybe propose a patch to add some doc sizes to
paper.scm that you think would be useful.  I know this was your
original plan, which I derailed with this landscape
investigation... sorry about that!

Cheers,
- Graham