ClutterBox is meant to work like the HTML boxing model: it has a margin and
a backgrdound color, and every child actor is added with a pack type and a
padding. The ClutterBoxChild structure holds the child actor, the padding,
the packing type and the allocated coordinates for the actor.
* clutter/clutter-types.h: Document ClutterGravity enumeration
and remove the only incomplete symbol of the api reference. Now
we are up to 79% documented symbols.
