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/private/fswatcher.h

@@ -62,7 +62,7 @@ public:
         if (!DoAdd(watch))
             return false;
 
-        // add watch to our map (always succeedes, checked above)
+        // add watch to our map (always succeeds, checked above)
         wxFSWatchEntries::value_type val(watch->GetPath(), watch);
         return m_watches.insert(val).second;
     }