More interface header reviews by Azriel Fasten, along with a simple item "add" group for wxSizer.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@53498 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

interface/sizer.h

@@ -767,6 +767,9 @@ public:
     */
     ~wxSizer();
 
+    /** @name Item Management */
+    //@{
+
     /**
         Appends a child to the sizer.
 
@@ -940,6 +943,8 @@ public:
     */
     wxSizerItem* AddStretchSpacer(int prop = 1);
 
+    //@}
+
     /**
         This method is abstract and has to be overwritten by any derived class.
         Here, the sizer will do the actual calculation of its children's minimal sizes.