Unify package version on VERSION file; bump abc2midi to 5.03 (#25)

- abc2midi 5.03 (April 2026): bumped #define VERSION in store.c to reflect this branch's accumulated fixes
(error exit status, missing C:/R:/X: header emission, %%MIDIdef macros allowed anywhere) plus the
build-system additions.
- Single source of truth for the package release date: the VERSION file is now consumed by both build
paths.
  - CMakeLists.txt reads it via file(STRINGS VERSION ABCMIDI_VERSION ...); the previously hard-coded
project(VERSION 2026.02.24) (an unused PROJECT_VERSION) is dropped because the date format isn't
MAJOR.MINOR.PATCH.
  - configure.ac uses m4_esyscmd_s([cat VERSION]) in AC_INIT, replacing the very stale hard-coded
2011-08-03.
  - The two build paths remain independent — no cross-generation between CMake and autoconf.
- Test normalization fix (tests/run_test.cmake): the version-banner regex now requires a capitalized month
and accepts a date with or without a day number. The previous regex was lowercase-permissive and silently
ate PostScript lines like 0.5 setlinewidth 0 0 moveto in yaps output — tests/golden/yaps_coleraine.txt is
regenerated to reflect the now-correctly-preserved PostScript.
- Docs:
  - doc/CHANGES: April 25 2026 entry covering the version bump and VERSION-file unification.
  - doc/readme.txt: per-tool listing updated (abc2midi 5.03 April 2026, midistats 1.03 February 20 2026
synced to source).
  - doc/abc2midi.1: header label bumped to 5.03 April 2026 (content not audited).
  - README.md: new Maintainers / releasing section documenting the release procedure, including the
requirement to run autoreconf -f so the committed configure picks up the new AC_INIT arguments.

doc/abc2midi.1

@@ -563,7 +563,7 @@ James Allwright <J.R.Allwright@westminster.ac.uk>
 .SH SUPPORTED
  by Seymour Shlien <fy733@ncf.ca>
 .SH VERSION
-This man page describes abc2midi version 2.27  June 25 2006.
+This man page describes abc2midi version 5.03 April 2026.
 .SH COPYRIGHT
 Copyright 1999 James Allwright
 .PP