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/longlong.h

@@ -707,7 +707,7 @@ public:
     wxLongLongWx operator-() const;
     wxLongLongWx& Negate();
 
-        // subraction
+        // subtraction
     wxLongLongWx operator-(const wxLongLongWx& ll) const;
     wxLongLongWx& operator-=(const wxLongLongWx& ll);