Document wxGenericAnimationCtrl XRC handler and it to XRC schema

It's actually the same handler as for wxAnimationCtrl, but it still
needs to be mentioned in the XRC format description and recognized by
its schema.

docs/doxygen/overviews/xrc_format.h

@@ -1185,6 +1185,14 @@ objects. If sizer child is used, it sets
     Ignored, preserved only for compatibility.}
 @endTable
 
+@subsubsection xrc_wxgenericanimationctrl wxGenericAnimationCtrl
+
+This handler is identical to the one for @ref xrc_wxanimationctrl
+"wxAnimationCtrl", please see it for more information. The only difference is
+that, for the platforms with a native wxAnimationCtrl implementation, using
+this handler creates a generic control rather than a native one.
+
+
 @subsubsection xrc_wxgenericdirctrl wxGenericDirCtrl
 
 @beginTable