More-itertools

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* New itertools
* :func:`mark_ends` (thanks to kalekundert)
* :func:`is_sorted`

* Changes to existing itertools:
* :func:`islice_extended` can now be used with real slices (thanks to cool-RR)
* The implementations for :func:`filter_except` and :func:`map_except` were improved (thanks to SergBobrovsky)

* Other changes
* Automated tests now enforce code style (using `black <https://github.com/psf/black>`__)
* The various signatures of :func:`islice_extended` and :func:`numeric_range` now appear in the docs (thanks to dsfulf)
* The test configuration for mypy was updated (thanks to blueyed)

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* New itertools
* :func:`zip_equal` (thanks to frankier and alexmojaki)

* Changes to existing itertools:
* :func:`split_at`, :func:`split_before`, :func:`split_after`, and :func:`split_when` all got a ``maxsplit`` parameter (thanks to jferard and ilai-deutel)
* :func:`split_at` now accepts a ``keep_separator`` parameter (thanks to jferard)
* :func:`distinct_permutations` can now generate ``r``-length permutations (thanks to SergBobrovsky and ilai-deutel)
* The :func:`windowed` implementation was improved (thanks to SergBobrovsky)
* The :func:`spy` implementation was improved (thanks to has2k1)

* Other changes
* Type stubs are now tested with ``stubtest`` (thanks to ilai-deutel)
* Tests now run with ``python -m unittest`` instead of ``python setup.py test`` (thanks to jdufresne)

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* Bug fixes
* The .pyi files for typing were updated. (thanks to blueyed and ilai-deutel)

* Changes to existing itertools:
* :func:`numeric_range` now behaves more like the built-in :func:`range`. (thanks to jferard)
* :func:`bucket` now allows for enumerating keys. (thanks to alexchandel)
* :func:`sliced` now should now work for numpy arrays. (thanks to sswingle)
* :func:`seekable` now has a ``maxlen`` parameter.

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* Bug fixes
* :func:`partition` works with ``pred=None`` again. (thanks to MSeifert04)

* New itertools
* :func:`sample` (thanks to tommyod)
* :func:`nth_or_last` (thanks to d-ryzhikov)

* Changes to existing itertools:
* The implementation for :func:`divide` was improved. (thanks to jferard)

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* Bug fixes
* The type stub files are now part of the wheel distribution (thanks to keisheiled)

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* Bug fixes
* The type stub files now work for functions imported from the
root package (thanks to keisheiled)