fixed @code sections

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@52256 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

docs/doxygen/overviews/app.h

@@ -54,12 +54,12 @@
 
  bool DerivedApp::OnInit()
  {
-   wxFrame *the_frame = new wxFrame(@NULL, ID_MYFRAME, argv[0]);
+   wxFrame *the_frame = new wxFrame(NULL, ID_MYFRAME, argv[0]);
    ...
-   the_frame-Show(@true);
+   the_frame->Show(true);
    SetTopWindow(the_frame);
 
-   return @true;
+   return true;
  }
  @endcode