More-itertools

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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)

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* New itertools and other additions
* This library now ships type hints for use with mypy.
(thanks to ilai-deutel for the implementation, and to gabbard and fmagin for assistance)
* :func:`split_when` (thanks to jferard)
* :func:`repeat_last` (thanks to d-ryzhikov)

* Changes to existing itertools:
* The implementation for :func:`set_partitions` was improved. (thanks to jferard)
* :func:`partition` was optimized for expensive predicates. (thanks to stevecj)
* :func:`unique_everseen` and :func:`groupby_transform` were re-factored. (thanks to SergBobrovsky)
* The implementation for :func:`difference` was improved. (thanks to Jabbey92)

* Other changes
* Python 3.4 has reached its end of life and is no longer supported.
* Python 3.8 is officially supported. (thanks to jdufresne)
* The ``collate`` function has been deprecated.
It raises a ``DeprecationWarning`` if used, and will be removed in a future release.
* :func:`one` and :func:`only` now provide more informative error messages. (thanks to gabbard)
* Unit tests were moved outside of the main package (thanks to jdufresne)
* Various documentation fixes (thanks to kriomant, gabbard, jdufresne)

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* New itertools
* :func:`distinct_combinations`
* :func:`set_partitions` (thanks to kbarrett)
* :func:`filter_except`
* :func:`map_except`

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* New itertools
* :func:`ichunked` (thanks davebelais and youtux)
* :func:`only` (thanks jaraco)

* Changes to existing itertools:
* :func:`numeric_range` now supports ranges specified by
``datetime.datetime`` and ``datetime.timedelta`` objects (thanks to MSeifert04 for tests).
* :func:`difference` now supports an *initial* keyword argument.


* Other changes
* Various documentation fixes (thanks raimon49, pylang)