CI and custom build script utilities

- macOS DMG image using AppDMG with custom background
- Linux AppImage
- Windows MSYS2 packaging
- Source code tarball including subprojects source code
- LHelper compatible build script

scripts/msys2-package.sh

@@ -0,0 +1,56 @@
+#!/bin/bash
+set -ex
+
+if [ ! -e "src/api/api.h" ]; then
+  echo "Please run this script from the root directory of Lite XL."
+  exit 1
+fi
+
+# FIXME: For some strange reason sometimes an error occurs randomly on the
+# MINGW32 build of GitHub Actions; the environment variable $INSTALL_NAME
+# is correct, but it expands with a drive letter at the end (all builds).
+
+show_help(){
+  echo
+  echo "Usage: $0 <OPTIONS>"
+  echo
+  echo "Available options:"
+  echo
+  echo "-b --builddir DIRNAME     Sets the name of the build directory (not path)."
+  echo "                          Default: 'build'."
+  echo "-d --destdir DIRNAME      Sets the name of the install directory (not path)."
+  echo
+}
+
+BUILD_DIR=build
+
+for i in "$@"; do
+  case $i in
+    -h|--belp)
+      show_help
+      exit 0
+      ;;
+    -b|--builddir)
+      BUILD_DIR="$2"
+      shift
+      shift
+      ;;
+    -d|--destdir)
+      DEST_DIR="$2"
+      shift
+      shift
+      ;;
+    *)
+      # unknown option
+      ;;
+  esac
+done
+
+if [[ -n $1 ]]; then
+  show_help
+  exit 1
+fi
+
+DESTDIR="$(pwd)/${DEST_DIR}" meson install --skip-subprojects -C ${BUILD_DIR}
+
+zip -9rv ${DEST_DIR}.zip ${DEST_DIR}/*