2.12.1 (stable)

Documentation:
* slot, signal: Describe the slot<void(int)> syntax more
  (Kjell Ahlstedt) Issue #86 (Daniel Boles)
* connection: Improve the class documentation
  (Kjell Ahlstedt) Issue #88 (Daniel Boles)
* Improve Visual Studio build documentation
  (Chun-wei Fan) Pull request #94
* Remove AUTHORS and add general information to README.md
  (Kjell Ahlstedt) Issue gtkmm#140

Build:
* Meson: Don't copy files with configure_file()
  (Kjell Ahlstedt)
* Meson: Fix the evaluation of is_git_build on Windows
  (Kjell Ahlstedt) Issue gtkmm#131 (William Roy)
* Visual Studio: Support static builds
  Issue #90 (Swat-SomeBug)
  (Chun-wei Fan) Pull request #92