3.89.4: (unstable)
Distro packagers should probably not package this yet.

Gtk:
* Add Gtk::WidgetCustomDraw and WidgetCustomSnapshot.
  These make it possible to use signal_draw() and snapshot_vfunc() in gtkmm
  without modification of gtk+.
  (Kjell Ahlstedt) Bug #775348. See also gtk+ bug 774778.
* Add Gtk::Snapshot.
  (Kjell Ahlstedt)
* Application: Remove create() method with argc,argv arguments.
  https://mail.gnome.org/archives/gtkmm-list/2017-February/msg00000.html
  (Kjell Ahlstedt)
* CellArea: Add snapshot() and snapshot_vfunc().
  (Kjell Ahlstedt)
* CellRenderer: Add snapshot() and snapshot_vfunc().
  (Kjell Ahlstedt)
* CellArea: Remove property_cell_area() and the constructor
  that takes a CellArea parameter.
  (Kjell Ahlstedt)
* CheckButton: Remove draw_indicator_vfunc().
  (Kjell Ahlstedt)
* CheckMenuItem: Add snapshot_indicator_vfunc().
  (Kjell Ahlstedt)
* Container: Remove show_all_children().
  (Widgets are now visible by default, unlike in gtkmm 3.)
  (Kjell Ahlstedt)
* Main:
  - Remove constructors that take (argc,argv) parameters.
  (Kjell Ahlstedt)
  - Remove add_gtk_option_group().
  (Kjell Ahlstedt)
* ToggleButton:
  - Move set/get_inconsistent() to CheckButton.
  - Move set/get_mode() to CheckButton, renaming it to set/get_draw_indicator().
  (Kjell Ahlstedt)
* Widget:
  - Add get_first_child(), get_last_child(), get_next_sibling(),
  get_prev_sibling(), snapshot_child(). Add property_css_name().
  (Kjell Ahlstedt)
  - Add compute_expand_vfunc(), queue_draw_region_vfunc(),
  queue_draw_child_vfunc().
  (Kjell Ahlstedt)
  - Remove show_all(), set/get_no_show_all(), show_all_vfunc(),
  property_no_show_all().
  (Widgets are now visible by default, unlike in gtkmm 3.)
  (Kjell Ahlstedt)
* Adapt various implementation code to changed GTK+ API.
  (Kjell Ahlstedt)