docs: Mention signal-swapped-after modifier
docs: Mention signal-swapped-after modifier

The signal-swapped-after:: modifier for signal connection inside the
clutter_actor_animate* variadic arguments functions is not mentioned in
the documentation.

GNOME/clutter,heysion/clutter-clone,nobled/clutter,Distrotech/clutter,spatulasnout/clutter,ebassi/clutter,djdeath/clutter-multithreaded,jigpu/clutter,collects/clutter,dlespiau/clutter,ebassi/clutter,rkudiyarov/clutter_osx,djdeath/clutter-multithreaded,djdeath/clutter,spatulasnout/clutter,rkudiyarov/clutter_osx,djdeath/clutter-android,heysion/clutter-clone,djdeath/clutter-android,kerrickstaley/clutter-vala,dlespiau/clutter,jigpu/clutter,collects/clutter,Distrotech/clutter,heysion/clutter-clone,spatulasnout/clutter,djdeath/clutter-android,rkudiyarov/clutter_osx,collects/clutter,Distrotech/clutter,jigpu/clutter,kerrickstaley/clutter-vala,GNOME/clutter,djdeath/clutter,GNOME/clutter,spatulasnout/clutter,djdeath/clutter,kerrickstaley/clutter-vala,kerrickstaley/clutter-vala,jigpu/clutter,Distrotech/clutter,collects/clutter,djdeath/clutter,djdeath/clutter-multithreaded,spatulasnout/clutter,dlespiau/clutter,rkudiyarov/clutter_osx,Distrotech/clutter,heysion/clutter-clone,djdeath/clutter-android,GNOME/clutter,djdeath/clutter,nobled/clutter,djdeath/clutter,ebassi/clutter,jigpu/clutter,Distrotech/clutter,nobled/clutter,ebassi/clutter,djdeath/clutter-multithreaded,GNOME/clutter,collects/clutter,jigpu/clutter,djdeath/clutter-android,ebassi/clutter,heysion/clutter-clone