* Fixed markup text kerning, see input/test/metronome.ly.
(Ugh, only feasible if kerning is first markup -- markup text should be revised.)
* Fixed molecule caching problem with stem-tremolo: fixes vertical
positioning of stem-tremolo.
* Added forced slur direction (stemUp no longer implies slurUp) in
cross-staff slur example.
* Fixes to Glissando and line-spanner. Behaves reasonably across line
breaks.
* Added: Align_interface::fixed_distance_alignment_callback that does
not compute the extents of the to-be-aligned objects. This delays many
brew_molecule() calls, because staff-height is no longer needed for
aligning.
* Bugfix: allows linebreaks for some types of beam.
* Bugfix: add braces in larger size range; prevents "Unknown character
127" messages, hopefully.