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*

interface/wx/config.h

@@ -894,7 +894,7 @@ public:
 
     For example:
     @code
-    // this function loads somes settings from the given wxConfig object;
+    // this function loads some settings from the given wxConfig object;
     // the path selected inside it is left unchanged
     bool LoadMySettings(wxConfigBase* cfg)
     {