atkmm 2.28.4 (stable):

Documentation:
* atkmm.h: Update link to ATK
  (Kjell Ahlstedt)
* Add README.win32.md with Win32 build documentation
  (Chun-wei Fan)
* Remove AUTHORS and add general information to README.md
  (Kjell Ahlstedt) Issue gtkmm#140

Meson build:
* Detect if we build from a git subtree
  (William Roy) Merge request gtkmm!72
* Don't copy files with configure_file()
  (Kjell Ahlstedt)
* Fix the evaluation of is_git_build on Windows
  (Kjell Ahlstedt) Issue gtkmm#131 (William Roy)
* Don't fail if warning_level=everything
  (Daniel Boles, Kjell Ahlstedt) Merge request gtkmm!87