More-itertools

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* New itertools:
* ``distribute`` (Thanks to mozbhearsum and coady)
* ``sort_together`` (Thanks to clintval)
* ``stagger`` and ``zip_offset`` (Thanks to joshbode)
* ``padded``
* Improvements to existing itertools:
* ``peekable`` now handles negative indexes and slices with negative
components properly.
* ``intersperse`` is now slightly faster. (Thanks to pylang)
* ``windowed`` now accepts a ``step`` keyword argument.
(Thanks to pylang)
* Python 3.6 is now supported.

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* Move docs 100% to readthedocs.io.

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* New itertools:
* ``accumulate``, ``all_equal``, ``first_true``, ``partition``, and
``tail`` from the itertools documentation.
* ``bucket`` (Thanks to Rosuav and cvrebert)
* ``collapse`` (Thanks to abarnet)
* ``interleave`` and ``interleave_longest`` (Thanks to abarnet)
* ``side_effect`` (Thanks to nvie)
* ``sliced`` (Thanks to j4mie and coady)
* ``split_before`` and ``split_after`` (Thanks to astronouth7303)
* ``spy`` (Thanks to themiurgo and mathieulongtin)
* Improvements to existing itertools:
* ``chunked`` is now simpler and more friendly to garbage collection.
(Contributed by coady, with thanks to piskvorky)
* ``collate`` now delegates to ``heapq.merge`` when possible.
(Thanks to kmike and julianpistorius)
* ``peekable``-wrapped iterables are now indexable and sliceable.
Iterating through ``peekable``-wrapped iterables is also faster.
* ``one`` and ``unique_to_each`` have been simplified.
(Thanks to coady)

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* Added ``one`` from ``jaraco.util.itertools``. (Thanks, jaraco!)
* Added ``distinct_permutations`` and ``unique_to_each``. (Contributed by
bbayles)
* Added ``windowed``. (Contributed by bbayles, with thanks to buchanae,
jaraco, and abarnert)
* Simplified the implementation of ``chunked``. (Thanks, nvie!)
* Python 3.5 is now supported. Python 2.6 is no longer supported.
* Python 3 is now supported directly; there is no 2to3 step.

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* Added ``iterate`` and ``with_iter``. (Thanks, abarnert!)

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* Added (tested!) implementations of the recipes from the itertools
documentation. (Thanks, Chris Lonnen!)
* Added ``ilen``. (Thanks for the inspiration, Matt Basta!)