Issue 4176: Add regtests for numbered and single-digit time signature styles
Doc: Issue 3879: Tag arguments may use dot separator
Doc: Issue 3877: clarify use of \lyricmode and variants
Issue 4112: Add internal chord-range option to part combiner

Add a number-pair parameter to make-part-combine-music to replace the
previously hard-coded minimum and maximum intervals that may be
combined into a chord or unison in the shared voice.

There is no user interface for this enhancement because it is not easy
to agree on one, but there is a regression test showing how it might
be used at one's own risk.
Doc: Default font size is 11pt

This was changed in 2005 from 12pt to 11pt.  However, the documentation
incorrectly talked about 10pt as the default..
Doc: Document unit of \abs-fontsize

This needs a special mentioning here since all global measurements are in
staff-spaces otherwise.
Add regtest for mensural and neomensural time signature styles.

Add regtest for "compound" time signatures that are merely simple
fractions and compound time signatures with simple-fraction
components.