optimise literal string case using a switch statement
enable switch transform for regular PrimaryCmpNode

native support for Py_UNICODE, coercion between 1-character unicode literals and Py_UNICODE, fix C iteration over unicode strings by using Py_UNICODE*

special case '=None' default arguments in ext arg type testing: automatically allow None in this case

faster way to test certain builtin types for truth: list, tuple, bytes, unicode; fix truth testing of bytes literals