Issue 3469: adding markup-commands \oval and \ellipse

\oval and \ellipse are drawing an oval respectively an ellipse around their
argument.
Also adding a reg-test for markup-commands framing their argument.

Signed-off-by: David Kastrup <dak@gnu.org>
Doc-fr: updates NR and community
Fix typos in the contributor's guide.
Fix *ly/*.scm typo.
Build: Search out dir before src dir (issue 3121).
Support for testing min and max versions of Guile.
Require 1.8.2 <= x < 1.9.0 where x=Guile version.

Guile 2 isn't supported yet. Guile 1.9.0 is the start of the
development branch that lead to Guile 2. See issue 3461.
Support for testing min and max versions of Python.
Require 2.4 <= x < 3.0 where x=Python version.

Python 3 isn't supported yet. See issue 3462.
Issue 3471: Allow decimal fractions with non-empty parts before and after '.' in music

This permits writing things like

mkMove = #(define-music-function
        (parser location x y)
        ( number? number? )
        #{ \once \override TextScript #'extra-offset = #(cons x y)
        #})

{
	\mkMove 4.4 -3.3
	c1^"XY"
}

Since integers are accepted in this kind of usage, not accepting
floating point numbers appears inconsistent.

While in INITIAL mode like inside of layout blocks real numbers can
be written like 4. or -.3 for historic reasons, permitting this inside
of music could easily lead to confusion with durations or
articulations, so those spellings remain invalid in music modes.

Decimal fractions are also not accepted in \chordmode since this would
preclude chord entry like c:13.11^3.7 and similar.
Corrections to LM (Issue 3407)
Release: bump VERSION_DEVEL.
PO: update template.
Release: update news.
Release: bump VERSION.
Revert "Issue 3449: Shift accordion register symbols down by half a line width"

This reverts commit cc57862cb46c7bf63f5f0b4740ea28eb597fd2be.
Issue 3476: Allow map-some-music to filter elements and articulations
Issue 3388: -dpreview retains non-working page links in table of contents

This just disables mark_page_link in the EPS header.  When including
EPS files in LilyPond itself, BeginEPSF and EndEPSF should limit the
effect of this redefinition to the EPS file itself, restoring the
userdict afterwards.
Issue 3472: several fixes to input/regression/scheme-text-spanner.ly

* The file `input/regression/scheme-text-spanner.ly' assigns a constant
pair to the variable `event-drul' and subsequently attempts to modify
the pair.  This can lead to scheme-text-spanners not appearing when
requested in simultaneous contexts.  This patch corrects the faulty usage,
replacing `event-drul' with two variables `event-start' and `event-stop'.

* The variable `current-event' is not necessary, and has been removed.

* Tabs in the engraver definition have been replaced with spaces.

Signed-off-by: David Kastrup <dak@gnu.org>
Issue 3449: Shift accordion register symbols down by half a line width

This makes the documented proposals for combining the accordion
register symbols together with the accordion dot symbol match in
positioning.  It would have been feasible instead to shift the
(centered) accordion dot, but some register symbols work with
different line widths.

The net result will now exhibit a slight descender (namely half a
linewidth) of the accordion register symbols when used in a running
line.