This module provides an implementation of the *set* and *frozenset* types which
were introduced in Python 2.4, but which work under older versions (Python 2.2
or 2.3). It is a standalone module written entirely in Python, and can easily
be used as a substitute for the built-in types when runing under older Pythons.
Care was taken to try to provide nearly 100% compatibility with Python 2.4's
behavior.