docs: gtk-doc fixes for Animator
docs: gtk-doc fixes for Animator

Fix the syntax for:

  → enumeration values
  → return values
  → @since tags

Also, fix the introspection annotations.

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