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/propgrid/propgrid.h

@@ -593,7 +593,7 @@ enum wxPG_INTERNAL_FLAGS
 // used to do the very same thing, but it hasn't been updated for a while
 // and it is currently deprecated.
 // Please note that most member functions are inherited and as such not
-// documented heree. This means you will probably also want to read
+// documented here. This means you will probably also want to read
 // wxPropertyGridInterface class reference.
 // To process input from a propertygrid control, use these event handler
 // macros to direct input to member functions that take a wxPropertyGridEvent