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/mimetype.h

@@ -32,7 +32,7 @@ class WXDLLIMPEXP_FWD_BASE wxIconLocation;
 class WXDLLIMPEXP_FWD_BASE wxFileTypeImpl;
 class WXDLLIMPEXP_FWD_BASE wxMimeTypesManagerImpl;
 
-// these constants define the MIME informations source under UNIX and are used
+// these constants define the MIME information source under UNIX and are used
 // by wxMimeTypesManager::Initialize()
 enum wxMailcapStyle
 {