This adds several new widgets that were added in GTK+: HeaderBar, ListBox, PlacesSidebar, SearchBar, and Stack. Thanks to Juan Rafael García Blanco, Andrew Potter, and Kjell Ahlstedt for that hard work.
It deprecates StockID, Table, IconFactory, IconSet, IconSource, and Gdk::Color along with several methods.
This glibmm release also has a fairly useable API for Gio::Menu and Gio::Action so you can really create gtkmm Menus with them and Gtk::Builder (here is an example). But unlike GTK+, we decided not to deprecate Gtk::UIManager, Gtk::Action and friends yet.
Most importantly, and most difficult to notice, we have deprecated deriving from Glib::Object before deriving from interface classes (such as Gtk::TreeModel). So you need to make changes such as this. The previous use of interface classes as the last base classes, after Glib::Object (which used to be the only way to use them) will cause runtime warnings in glib for now, and will probably break your application’s functionality in future glib versions. It’s not what we want.