Add `Tooltip` stub
Add `Tooltip` stub

gkoz/gtk-rs-gtk,EPashkin/rust-gnome-gtk,daa84/gtk,gkoz/rust-gnome-gtk,EPashkin/rust-gnome-gtk,daa84/gtk,gkoz/rust-gnome-gtk,rust-gnome/gtk,gkoz/gtk-rs-gtk,Susurrus/gtk,Susurrus/gtk,rust-gnome/gtk