news gtk+ widgets (=> update doc (gtk3.doc?))

[Thierry Vignaud]

3,12 :
GtkActionBar — A full width bar for presenting contextual actions
GtkFlowBox — A container that allows reflowing its children
GtkPopover — Context dependent bubbles


3,14 : no new widget

Gtk 3,16
GtkGLArea — A widget for custom drawing with OpenGL
GtkModelButton — A button that uses a GAction as model
GtkStackSidebar — An automatic sidebar widget
GtkPopoverMenu — Popovers to use as menus