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/dc.h

@@ -528,7 +528,7 @@ public:
 
     virtual void ComputeScaleAndOrigin();
 
-    // this needs to overidden if the axis is inverted
+    // this needs to overridden if the axis is inverted
     virtual void SetAxisOrientation(bool xLeftRight, bool yBottomUp);
 
     virtual double GetContentScaleFactor() const { return m_contentScaleFactor; }