StableSet: Pointing to a new implementation

[idanmiara]

Hi,

I wanted to point out that I made an implementation of OrderedSet that uses the same foundations as your implementation but adds many more features.
(I called it StableSet, as OrderedSet was a name for a different implementation) .
I also used your tests to test full compatibility between your implementation and 2 other implementations.

Please have a look if you are interested:
https://pypi.org/project/stableset/

I made a PR to merge it upstream:
https://github.com/rspeer/ordered-set/pull/92/files