Implement basic testing infrastructure (#19)

* Add configuration for CMake build system alongside autoconf

- Add a modern CMake build system (`CMakeLists.txt`, `CMakePresets.json`) that coexists with the legacy
autoconf/Makefile build
- Shared source files (`midifile.c`, `parseabc.c`, `music_utils.c`, `parser2.c`) are compiled once via OBJECT
libraries and linked into the 8 binaries
- Three presets: `default` (Release), `debug`, `sanitize` (ASan + UBSan)
- Generates `compile_commands.json` for clangd/LSP editor support
- Install rules match the legacy Makefile (binaries, doc files, man pages)
- Pinned to `-std=gnu89` because the codebase mixes K&R `()` and ANSI typed prototypes — in C23/gnu23 (GCC 15+
default), `()` means `(void)`, making these a hard error. Note: **the existing autoconf build is also broken with
GCC 15** for the same reason

```sh
cmake --preset debug
cmake --build --preset debug
cmake --install build/debug --prefix /usr/local

Documentation

- README.md: added Building section with both autoconf and CMake instructions
- doc/readme.txt: added build instructions in the existing preamble
- doc/CHANGES: added changelog entry

Test plan

- All 3 presets configure and build with GCC 15
- Smoke test: abc2midi samples/coleraine.abc produces valid MIDI through mftext
- Sanitizer build (--preset sanitize) runs clean on sample files
- Install layout verified: 8 binaries, 10 doc files, 8 man pages in correct paths
- Build on macOS (untested, should work with AppleClang)

* Implement basic testing infrastructure

The CMake build includes a test suite covering all 8 programs:

- **Smoke tests** verify each binary runs cleanly with `-ver`.
- **Golden-file tests** run each program on a sample input and compare the
  (normalized) output to a checked-in reference. Binary MIDI outputs are
  piped through `mftext` to produce diffable text. Volatile lines (version
  banners, dates, temporary paths) are stripped before comparison.

```sh
ctest --preset debug

ctest --preset debug -L golden
ctest --preset debug -L smoke
```

To regenerate the golden files after an intentional behavioural change,
review the diff, then commit:

```sh
cmake --build build/debug --target update-golden
git diff tests/golden/
```

* Factorize more the test CMake code

CMakeLists.txt

@@ -0,0 +1,149 @@
+cmake_minimum_required(VERSION 3.14)
+
+# Read version from the VERSION file, matching the existing convention
+file(STRINGS VERSION ABCMIDI_VERSION_STRING LIMIT_COUNT 1)
+
+project(abcmidi
+  VERSION 2026.02.24
+  DESCRIPTION "ABC music notation tools: converters between ABC, MIDI, and PostScript"
+  LANGUAGES C
+)
+
+# Modern CMake: export compile_commands.json for clangd/LSP
+set(CMAKE_EXPORT_COMPILE_COMMANDS ON)
+
+# Default to Release if not specified
+if(NOT CMAKE_BUILD_TYPE AND NOT CMAKE_CONFIGURATION_TYPES)
+  set(CMAKE_BUILD_TYPE Release CACHE STRING "Build type" FORCE)
+  set_property(CACHE CMAKE_BUILD_TYPE
+    PROPERTY STRINGS Debug Release RelWithDebInfo MinSizeRel)
+endif()
+
+# --- Options ---
+
+option(ABCMIDI_SANITIZERS "Enable AddressSanitizer and UndefinedBehaviorSanitizer" OFF)
+
+# --- Compiler configuration ---
+
+# Common compile options applied to every target via an INTERFACE library
+add_library(abcmidi_common INTERFACE)
+
+target_compile_definitions(abcmidi_common INTERFACE
+  ANSILIBS
+)
+
+# The codebase mixes K&R empty-parens "()" (meaning unspecified args) with
+# ANSI typed prototypes.  In C23/gnu23 (GCC 15+ default), "()" means "(void)",
+# making these a hard error.  Pin to gnu89 until the ANSI migration is complete,
+# then switch to c_std_11 or later.
+target_compile_options(abcmidi_common INTERFACE
+  $<$<C_COMPILER_ID:GNU,Clang,AppleClang>:
+    -std=gnu89
+    -Wall
+  >
+)
+
+if(ABCMIDI_SANITIZERS)
+  target_compile_options(abcmidi_common INTERFACE
+    -fsanitize=address,undefined -fno-omit-frame-pointer)
+  target_link_options(abcmidi_common INTERFACE
+    -fsanitize=address,undefined)
+endif()
+
+# --- Shared object libraries (compiled once, linked into multiple binaries) ---
+
+add_library(obj_midifile OBJECT midifile.c)
+target_link_libraries(obj_midifile PUBLIC abcmidi_common)
+
+add_library(obj_parseabc OBJECT parseabc.c music_utils.c)
+target_link_libraries(obj_parseabc PUBLIC abcmidi_common)
+
+add_library(obj_parser2 OBJECT parser2.c)
+target_link_libraries(obj_parser2 PUBLIC abcmidi_common)
+
+# --- Executables ---
+
+# abc2midi: ABC notation → MIDI
+add_executable(abc2midi
+  store.c genmidi.c queues.c stresspat.c
+)
+target_link_libraries(abc2midi PRIVATE
+  obj_parseabc obj_parser2 obj_midifile abcmidi_common m)
+
+# abc2abc: ABC notation → ABC notation (transposition, reformatting)
+add_executable(abc2abc toabc.c)
+target_link_libraries(abc2abc PRIVATE obj_parseabc abcmidi_common m)
+
+# midi2abc: MIDI → ABC notation
+add_executable(midi2abc midi2abc.c)
+target_link_libraries(midi2abc PRIVATE obj_midifile abcmidi_common m)
+
+# midistats: MIDI file statistics
+add_executable(midistats midistats.c)
+target_link_libraries(midistats PRIVATE obj_midifile abcmidi_common m)
+
+# mftext: MIDI → human-readable text
+add_executable(mftext mftext.c crack.c)
+target_link_libraries(mftext PRIVATE obj_midifile abcmidi_common m)
+
+# yaps: ABC notation → PostScript
+add_executable(yaps
+  yapstree.c drawtune.c debug.c pslib.c position.c
+)
+target_link_libraries(yaps PRIVATE
+  obj_parseabc obj_parser2 abcmidi_common m)
+
+# midicopy: MIDI file filtering/extraction
+add_executable(midicopy midicopy.c)
+target_link_libraries(midicopy PRIVATE abcmidi_common m)
+
+# abcmatch: ABC tune matching/comparison
+add_executable(abcmatch abcmatch.c matchsup.c)
+target_link_libraries(abcmatch PRIVATE obj_parseabc abcmidi_common m)
+
+# --- Install ---
+
+include(GNUInstallDirs)
+
+set(ABCMIDI_BINARIES abc2midi abc2abc midi2abc midistats mftext yaps midicopy abcmatch)
+
+install(TARGETS ${ABCMIDI_BINARIES}
+  RUNTIME DESTINATION ${CMAKE_INSTALL_BINDIR}
+)
+
+# Match the legacy Makefile: install only top-level doc files, not subdirectories
+install(FILES
+  doc/abcguide.txt
+  doc/abcmatch.txt
+  doc/gpl.txt
+  doc/history.txt
+  doc/hudsonshift.txt
+  doc/readme.txt
+  doc/yapshelp.txt
+  doc/AUTHORS
+  doc/CHANGES
+  VERSION
+  DESTINATION ${CMAKE_INSTALL_DOCDIR}
+)
+
+install(FILES
+  doc/abc2abc.1
+  doc/abc2midi.1
+  doc/abcmatch.1
+  doc/mftext.1
+  doc/midi2abc.1
+  doc/midicopy.1
+  doc/midistats.1
+  doc/yaps.1
+  DESTINATION ${CMAKE_INSTALL_MANDIR}/man1
+)
+
+# --- Tests ---
+
+include(CTest)
+if(BUILD_TESTING)
+  add_subdirectory(tests)
+endif()
+
+# TODO: install-validation test that verifies all binaries, doc files, and man
+# pages are installed to the expected paths.