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.
the inplace operators. The strategy is to have the operator overloading
code do the work and then to define equivalent method calls which rely on
the operators. The changes facilitate proper application of TypeError
and NonImplementedErrors.
Added corresponding tests to the test suite to make sure both the operator
and method call versions get exercised.
Add missing tests for difference_update().