Use calling syntax on Enum/IntEnum instead of make()

When PEP 435 is accepted, `enum.make()` may not be the best spelling. We can't put a classmethod on Enum since this will collide with the enum value namespace. One thought is to co-opt calling syntax for this purpose, e.g.

Animals = Enum('Animals', 'ant bee cat'.split())

or

People = IntEnum('People', 'anne bill cate dave elly'.split())

We'd probably want to deprecate single argument calling, which is pretty redundant anyway with getitem syntax.