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/event.h

@@ -2190,7 +2190,7 @@ public:
             *ypos = GetY();
     }
 
-    // This version if provided only for backwards compatiblity, don't use.
+    // This version if provided only for backwards compatibility, don't use.
     void GetPosition(long *xpos, long *ypos) const
     {
         if (xpos)