Add unfold-repeats-fully function which will expand repeats in the data
Implement event-chord-reduce for reducing chords to single notes
Issue 3682/1: Implement \beamExceptions function fishing exceptions from beamed music.
Issue 3682/2: Change documentation and regtests for \beamExceptions
let RhythmicStaff use default barline extent

There is no reason to make barlines in RhythmicStaff special.
The purpose of the deleted code was probably to ensure that
the barlines were visible at all (despite the fact that there
is just one staffline in a RhythmicStaff).  However, currently
barline code takes care of this by default.

This makes barlines in DrumStaff and RhythmicStaff similar.

A comment by Keith:
The book by Kurt Stone happens to have some bar-lines in single-line percussion
staves that are as tall as a 4/4 time-signature.  Other examples in the same
book have short bar-lines like these here, and looking at some scores the short
bar-lines are more common.
Issue 3694: Use standard inclusion scheme for FreeType headers.

The most recent FreeType release (2.5.1) has changed locations for header
files.  Using the standard way, this is not visible to applications.
Support properties on articulations.

Shorthand articulations like -. can now be ArticulationEvents, not just
articulation names. Previously a shorthand created a new ArticulationEvent
with its name, so there was no way to give it properties. Now it can be (and
is, by default) an ArticulationEvent.

Note that redefining a shorthand to a string (e.g. dashDot = "staccatissimo")
still creates propertyless articulations, regardless of \staccatissimo.
Support articulations and breaths in MIDI. (issue 3664)

Articulations and breaths can alter the length and volume of the note.
(Breaths affect the previous chord.) This is controlled by their
midi-length and midi-extra-velocity properties. The standard articulations
now have these properties where appropriate.

(seconds->moment s context) is a convenience function for making
absolute durations.