GtkSpinButton: Document some signals
GtkSpinButton: Document some signals

Based on a patch by Gergely Polonkai,
https://bugzilla.gnome.org/show_bug.cgi?id=733174

Adamovskiy/gtk,Lyude/gtk-,jadahl/gtk,chergert/gtk,Adamovskiy/gtk,alexlarsson/gtk,chergert/gtk,davidgumberg/gtk,chergert/gtk,jadahl/gtk,jigpu/gtk,ahodesuka/gtk,jigpu/gtk,jigpu/gtk,ahodesuka/gtk,davidgumberg/gtk,Lyude/gtk-,jadahl/gtk,ahodesuka/gtk,davidgumberg/gtk,alexlarsson/gtk,Adamovskiy/gtk,alexlarsson/gtk,Lyude/gtk-,jigpu/gtk,alexlarsson/gtk,jadahl/gtk,jessevdk/gtk,chergert/gtk,jessevdk/gtk,jigpu/gtk,chergert/gtk,alexlarsson/gtk,alexlarsson/gtk,ahodesuka/gtk,davidgumberg/gtk,jessevdk/gtk,Adamovskiy/gtk,jadahl/gtk,grubersjoe/adwaita,davidgumberg/gtk,jessevdk/gtk,jadahl/gtk,ahodesuka/gtk,Adamovskiy/gtk,chergert/gtk,Lyude/gtk-,grubersjoe/adwaita,ahodesuka/gtk,jadahl/gtk,chergert/gtk,jessevdk/gtk,alexlarsson/gtk,jigpu/gtk,Lyude/gtk-,jadahl/gtk,grubersjoe/adwaita,davidgumberg/gtk,Lyude/gtk-,jigpu/gtk,grubersjoe/adwaita,davidgumberg/gtk,Lyude/gtk-,davidgumberg/gtk,Adamovskiy/gtk,grubersjoe/adwaita,Adamovskiy/gtk,grubersjoe/adwaita,Lyude/gtk-,grubersjoe/adwaita,ahodesuka/gtk,jigpu/gtk,Adamovskiy/gtk,jessevdk/gtk,jessevdk/gtk,alexlarsson/gtk,grubersjoe/adwaita,chergert/gtk,ahodesuka/gtk