A few bugfixes since 8.13.0:
- fix im7 feature detection in meson
- add a summary table at the end of configure in meson
- fix libpng fallback when spng is disabled in meson
- add "unlimited" to jpegload
- better 0 detection in unpremultiply
- fix low bitdepth spng save [jeffska]
- fix PNG low bitdepth save of high bitdepth images
- add support for libjxl 0.7 [kleisauke]
- improve compatibility with older libgsf versions [kleisauke]