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/qt/window.h

@@ -50,7 +50,7 @@ class WXDLLIMPEXP_FWD_CORE wxQtShortcutHandler;
  * found in winevent_qt.(h|cpp) to send all Qt events here to QtHandleXXXEvent()
  * methods. All these methods receive the Qt event and the handler. This is
  * done because events of the containers (the scrolled part of the window) are
- * sent to the same wxWindow instance, that must be able to differenciate them
+ * sent to the same wxWindow instance, that must be able to differentiate them
  * as some events need different handling (paintEvent) depending on that.
  * We pass the QWidget pointer to all event handlers for consistency.
  */