Report lack of <dfn> for <span>s without attributes

Only do this when the <span> has no attributes as using the
lang/class/id attributes should continue to be okay.

Fixes #33.

src/wattsi.pas

@@ -451,7 +451,7 @@    TCrossReferences = record
          CrossRefListNode^.Topic := CrossReferenceName;
          CrossRefListNode^.LastHeading := LastSeenHeadingID;
          CrossRefListNode^.Element := Element;
-         if (Element.HasAttribute(kCrossRefAttribute) or Element.IsIdentity(nsHTML, eCode)) then
+         if (Element.HasAttribute(kCrossRefAttribute) or Element.IsIdentity(nsHTML, eCode) or (Element.IsIdentity(nsHTML, eSpan) and not Assigned(Element.Attributes))) then
             CrossRefListNode^.Kind := crExplicit
          else
             CrossRefListNode^.Kind := crImplicit;