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/stackwalk.h

@@ -143,7 +143,7 @@ public:
 #endif // wxUSE_ON_FATAL_EXCEPTION
 
 protected:
-    // this function must be overrided to process the given frame
+    // this function must be overridden to process the given frame
     virtual void OnStackFrame(const wxStackFrame& frame) = 0;
 };