This reverts commit b6788153161b4e07fbf3d42a2d8921ea049305d0.
There's no gdk-pixbuf3 anymore. gdk-pixbuf was separated from GTK+
and will stay at version 2.0 for GTK+ 3.0.
Link to properties. Correct titles for examples. Document a few trivial cases. Keep lists in section file and docs/plugins/Makefile.am alphabetically ordered. Fix warnings that gtk-doc points out.