Log Message:
mm-common: update to 1.0.3.

mm-common 1.0.3 (2021-05-20)

Meson build:
* Make it possible to use mm-common as a subproject
  (Kjell Ahlstedt)
* extra-install-cmd.py: Ignore FileNotFoundError
  (Kjell Ahlstedt)
* Make quiet installations possible
  (Kjell Ahlstedt)

Skeletonmm:
* Fix versioning on macOS
  (Kjell Ahlstedt) Pull request sigc++!65 (Tom Schoonjans)
* Use relative paths to untracked/
  (Kjell Ahlstedt) Merge request gtkmm!61 (Mingli Yu)
* Update dependencies in Meson build files:
  glibmm-2.4 -> glibmm-2.68, sigc++-2.0 -> sigc++-3.0
  (Kjell Ahlstedt)
* Make it possible to use skeletonmm as a subproject
  (Kjell Ahlstedt)