Issue 3806: add link to 2.16 manuals
Release: bump VERSION_DEVEL.
PO: update template.
Release: update news.
Doc: Issue 3807: More accurate wording for \version instructions
Merge remote branch 'origin/release/unstable' into HEAD
Release: bump VERSION.
Issue 3815: Parser: harmonize \lyricsto and \addlyrics arguments

Previously, they allowed arbitrary music but since that required looking
at lookahead tokens in the wrong mode, it led to strange errors like with
lyr=\lyricsto A { }
mus={c}
when mus= was parsed as a single token in lyrics mode.  Now both \addlyrics
and \lyricsto accept merely the same kind of delimited argument list
that \lyrics or \chords accept.  Additionally, to preserve compatibility
to a lot of examples, music identifiers like \mus are permitted as the
argument to \lyricsto and \addlyrics.

Since this requires a change in existing uses, this includes a
convert-ly rule that removes redundant uses of \lyricmode and
rearranges the combination with context starters such that \lyricsto
in general is applied last, like \lyricmode would be.
Run scripts/auxiliar/update-with-convert-ly.sh
Merge branch 'issue3815' into staging
Doc: Issue 3816: Explain placement of \breathe

  Also run convert-ly first
Revert "Doc: NR - convert A13 from scm to verbatim"

This reverts commit 9479135c586c5166051d118cabeeb9dce3b2fe9c.

This change got pushed by mistake. Apologies.