Single-note tremolos

[Carl Sorensen]

Dave Higgins noted that for notes outside of the staff, tremolo
indications collided with ledger lines.

In reviewing Gould (p. 222), I found several defaults in LilyPond that go
against Gould's recommendations.

1) The tremolo lines are too wide (they should be only as wide as a
crotchet note head).

2) The tremolo lines are too thick (they should be thinner than beams, but
in LilyPond they are the same thickness).

3) The tremolo lines collide with ledger lines (they should lie entirely
within the staff).

4) For notes on a staff line, the tremolo line closest to the heads
centered on a staff space.  This is allowed in Gould, but not recommended.
The recommendation is that single tremolo strokes should center on a staff
line.  The closest stroke and the single stroke are in the same position
in LilyPond, so I think it is best to move them to a staff line.

I have created changes to the semibreve single-note tremolo spacing code
to fix all of these issues. I've attached pdf output from the current code
as well as the improved code, along with my test file.

Please review the changes and let me know if you think this is worth
committing to LilyPond.

Thanks,

Carl

tremolo-test.pdf
Description: tremolo-test.pdf

tremolo-test.ly
Description: tremolo-test.ly

tremolo-test-improved.pdf
Description: tremolo-test-improved.pdf