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/univ/stdrend.h

@@ -269,7 +269,7 @@ protected:
         // draw complete rectangle
     void DrawRect(wxDC& dc, wxRect *rect, const wxPen& pen);
 
-        // draw the rectange using the first pen for the left and top sides
+        // draw the rectangle using the first pen for the left and top sides
         // and the second one for the bottom and right ones
     void DrawShadedRect(wxDC& dc, wxRect *rect,
                         const wxPen& pen1, const wxPen& pen2);