This consists of a meson option that
- sets a flag to make Aegisub read paths relative to the executable
- makes meson set up the symlinks like AppRun and .DirIcon as following
the AppDir format
and a CI workflow that builds with this option, installs to an AppDir
directory, and bundles it as an AppImage.
Modified from arch1t3cht/Aegisub#12 .
Co-authored-by: Fred Brennan <copypaste@kittens.ph>