0.9.0

• Project: officially place the project in maintenance mode, more details in readme
• API: add gtk_layer_try_force_commit()
• Fix: unmap tooltips of popups in correct order, fixes #178
• Fix: handle xdg_wm_base::ping, don't get labled as unresponsive
• Compat: bump supported GTK to v3.24.43
• Compat: NOTE: GTK v3.24.44 may break previous versions of gtk-layer-shell and work with this one, but we won't know for sure until it's released