Doc: simplify example changing default fonts (3027)

  The original function required the global staff size
  to be re-entered as myStaffSize, but this can be calculated
  from the value of staff-height, so avoiding having to
  replicate the value.
Typo in time-signature-settings.scm

Fixing missing space in commented example

issue 3074
Enhancement: 2 new markup-cmds: draw-dashed-line; draw-dotted-line

Issue 3071

Also includes Regression Test.
Thanks also to David Nalesnik for suggestions
Issue 677: \score markup confuses paper settings

I actually have no idea whether this is the right fix, but it seems to
do something related to the TODO comments and the issue report.
Issue 2990: \RemoveEmptyStaves in StaffGroup context crashes

The problem is caused by multiple axis group engravers, and in
particular nested VerticalAxisGroup grobs in connection with the
skyline code.  An extensive fix catching any recursive grob definition
will lead to quite more cryptic error messages rather than this
hand-tailored fix for the special case of VerticalAxisGroup nesting.

The solution chosen here is to complain when a VerticalAxisGroup is
announced from a subordinate context and let the current group commit
suicide.
Issue 3050: displayLilyMusic produced erroneous code for rightHandFinger arguments
Issue 3082: Let ChordNameVoice use the same performers as Voice

In particular, ties should be heeded when creating Midi from a
ChordNames context as they result in the omission of the engraved
chord name if an identical chord follows.  Reasoning for beams and
slurs is fuzzier, but an articulation different from the same music in
a regular Voice context does not seem to make sense.
Add different durations to input/regression/fretboard-chordchanges.ly
Issue 3083: Chord change detection in fretboards should depend on placements, not notes
Fix assertion failure (#2983).
Doc: add Known issue limiting calculation of LilyPond rationals (3084)
Doc: Update documentation of \once (2952)

  Bring documentation in line with committish
  ddce9767f975c989800cb99e003039a8bf050b45
  by removing statements that limit the use of
  \once to bare \override and \set commands.
Update bug squad rota
Shows ligature bracket extenders by setting bracket-visibility to ##t.

This bypasses the automatic visibility tests which are done mostly for
tuplet brackets.  In the future, it would be good to make a unified
system for brackets in which the tuplet bracket is one of several instead
of the "model" bracket.
Makes all side-positioning based on skylines instead of boxes.

The major work is in side-position-interface.cc, with minor
modifications at several places in the code-base to adapt to this.

This allows for snugger positioning of horizontally-oriented
fingerings.

A side-effect of this patch is that side-positioning of all
cross-staff grobs delves into the element list of axis-groups
in order to better guess position, which results in less
collisions (for example, dynamics are less likely to collide
with cross-staff beams).
articulate TremoloEvent

Expand TremoloEvent to repeated notes, in the unfolding stage of
articulation.
Doc: Add draw-dashed/dotted line cmds to changes

Example taken from reg test in Issue 3071
PO: update template.
Release: update news.
Release: bump version.