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/gtk1/toplevel.h

@@ -101,7 +101,7 @@ public:
     long          m_gdkFunc,
                   m_gdkDecor;
 
-    // private gtk_timeout_add result for mimicing wxUSER_ATTENTION_INFO and
+    // private gtk_timeout_add result for mimicking wxUSER_ATTENTION_INFO and
     // wxUSER_ATTENTION_ERROR difference, -2 for no hint, -1 for ERROR hint, rest for GtkTimeout handle.
     int m_urgency_hint;