#6 'cls' deserves pseudo-keyword status, same as 'self'

[szplug]

It's a quick and easy addition, but, 'cls' should be a
pseudo-keyword too since it is the convention for the
class argument for class methods, like 'self' is the
convention for the instance argument with instance
methods. Eg,

class Foo(object):
def summat(cls, x):
.....
summat = classmethod(summat)

....