… 3.7 (Python 3.8 is the new minimum)

…atures

- Added a StableSet implementation, as a base class for OrderedSet.
- Added Many functions to OrderedSet, to be more complete and more compatible with other implementations.
  - popitem(last: bool = True), similar to `dict.popitem` (note minor incompatibility with another implementation (`orderedset`) that have the `last` keyword in the `pop` function)
  - move_to_end(key), similar to `dict.move_to_end`
  - __le__, __lt__, __ge__, __gt__ - to improve subset/superset testing
- Minimum Python version is 3.8 (because __reversed__)
- Fix: OrderedSet.update now raised a TypeError instead of a ValueError when the type of the input is incorrect

…ils from __init__.py

test/__init__.py added

…ent tests

…ts to test multiple set types

…vall/orderedset/blob/master/tests/test_orderedset.py

…est` to `pytest`

…m/simonpercivall/orderedset/blob/master/tests/test_orderedset.py to test against multiple set types

…rdered-set-37/blob/master/test/test_testing.py _test_mypy.py - added from https://github.com/bustawin/ordered-set-37/blob/master/test/_test_mypy.py

…/bustawin/ordered-set-37/blob/master/test/test_testing.py to test against multiple set types

…at once

… implementations