docs/cookbook: Mention the event control macros
docs/cookbook: Mention the event control macros

Now that we have symbolic names for event propagation values for signal
handlers, we ought to mention them in the cookbook.

djdeath/clutter-multithreaded,Distrotech/clutter,djdeath/clutter,GNOME/clutter,heysion/clutter-clone,Distrotech/clutter,djdeath/clutter-multithreaded,ebassi/clutter,ebassi/clutter,collects/clutter,heysion/clutter-clone,collects/clutter,djdeath/clutter-android,djdeath/clutter-android,djdeath/clutter,GNOME/clutter,djdeath/clutter-android,collects/clutter,jigpu/clutter,kerrickstaley/clutter-vala,kerrickstaley/clutter-vala,djdeath/clutter,jigpu/clutter,djdeath/clutter,Distrotech/clutter,jigpu/clutter,jigpu/clutter,djdeath/clutter-multithreaded,heysion/clutter-clone,Distrotech/clutter,ebassi/clutter,djdeath/clutter,kerrickstaley/clutter-vala,heysion/clutter-clone,djdeath/clutter-multithreaded,GNOME/clutter,djdeath/clutter-android,djdeath/clutter,ebassi/clutter,Distrotech/clutter,djdeath/clutter-android,heysion/clutter-clone,GNOME/clutter,kerrickstaley/clutter-vala,collects/clutter,jigpu/clutter,GNOME/clutter,Distrotech/clutter,jigpu/clutter,ebassi/clutter,collects/clutter