Concave beams (was: free LilyPond advertising)

[Rune Zedeler]

Han-Wen Nienhuys skrev:
> This is pretty obvious for single-voice notes; for chords it gets
> hairier: which part of the chord notes do we use to decide this?

I think we should look at both top notes and bottom notes. We should
only make the beam horizontal if they agree that the pattern is concave.
(I.e. form a pattern of the top notes. Form another pattern of the
bottom notes. If both patterns are concave then make the beam horizontal)

If we have something like { \stemUp c d <e g> f } Then we do not want a
horizontal beam.

-Rune