consistent across versions.
* Relaxed the argument restrictions for non-operator methods. They now
allow any iterable instead of requiring a set. This makes the module
a little easier to use and paves the way for an efficient C
implementation which can take better advantage of iterable arguments
while screening out immutables.
* Added a PendingDeprecationWarning for Set.update() because it now
duplicates Set.union_update()
* Adapted the tests and docs to include the above changes.
* Added more test coverage including testing identities and checking
to make sure non-restartable generators work as arguments.
underlying dictionaries, there were no reasonable use cases (lexicographic
sorting of a list of sets is somewhat esoteric). Frees the operators
for other uses (such as strict subset and superset comparisons).
Updated documentation and test suite accordingly.
