Doc-it: update
Release: bump VERSION_DEVEL.
PO: update template.
Release: update news.
Release: bump VERSION.
Remove unused data from Completion_heads_engraver and Completion_rest_engraver
Issue 3593: Announce ends of ties in Completion_heads_engraver
Issue 3115: Revert "Uses a heuristic to determine if chord tremolos collide with accidentals."

This reverts commit d8dfa746ead381a80901106b9c9b079dc9b5d004.

Conflicts:
	scm/define-grobs.scm

But reconstitute input/regression/chord-tremolo-accidental.ly.  Not
done in a separate commit in order to preserve blame.
Build: perl-less build isn't supported (issue 3578).

Although labelled as optional, perl is required to build the
.pfb font files, which are not included in the tarball. With
this commit, perl becomes a required dependency.
Build: Bison is a required dependency again (issue 3577).
Build: Fix dependencies for ly-grammar.txt (issue 3577).
Build: Target version.itexi and weblinks.itexi (issue 3576).

Add the file extension and remove a pair of duplicated rules.
Issue 3604: Fix function signature of overrideTimeSignatureSettings

Using fraction? rather than pair? is more discriminative, and using
the cheap-list? predicate rather than plain list? is not really a
significant time saver in a complex construct like this.
Doc: Color the Attic link (issue 3596).

This seems to be necessary each time a section is added.
Doc: Update authors (issue 3597).
Doc-es: typo.
Doc: Relayout the download pages (issue 3595).

This slightly modifies the layout of the download pages to make
them more balanced (in the HTML version) and to accomodate wide
pictures.

For Unix, the "Specific packages" box is moved to the top right,
next to the "Generic packages" box, while the "Compiling a file"
box is now a centered, full-width box.

For MacOS and Windows, a similar change is made: the "Compiling a
file" box is moved below and turned into a centered, full-width box
to better accomodate the picture-full content.
Detect use of backslash in node names (3590)

Although a backslash in a node name appears to cause
no problems when used in a within-manual reference,
it causes cross-manual references to fail.
Doc: Remove backslash from all node names and references (3590)

  English docs only
Doc: add instructions for headings which include backslash (3590)

  and tidy up the formatting a little