Fix spelling in comments and documentation using codespell

Apply the utility from https://github.com/codespell-project/codespell/
to fix spelling issues in the headers under both include and interface
directories and add a file with a couple of exceptions.

The exact command line used was:

    $ codespell -w -I misc/scripts/codespell.ignore -i 3 in*

include/wx/vscroll.h

@@ -133,7 +133,7 @@ public:
     void HandleOnMouseWheel(wxMouseEvent& event);
 #endif // wxUSE_MOUSEWHEEL
 
-    // these functions must be overidden in the derived class to return
+    // these functions must be overridden in the derived class to return
     // orientation specific data (e.g. the width for vertically scrolling
     // derivatives in the case of GetOrientationTargetSize())
     virtual int GetOrientationTargetSize() const = 0;