More-itertools

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* New itertools:
* :func:`numeric_range` (Thanks to BebeSparkelSparkel and MSeifert04)
* :func:`count_cycle` (Thanks to BebeSparkelSparkel)
* :func:`locate` (Thanks to pylang and MSeifert04)
* Improvements to existing itertools:
* A few itertools are now slightly faster due to some function
optimizations. (Thanks to MSeifert04)
* The docs have been substantially revised with installation notes,
categories for library functions, links, and more. (Thanks to pylang)

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* Removed itertools:
* ``context`` has been removed due to a design flaw - see below for
replacement options. (thanks to NeilGirdhar)
* Improvements to existing itertools:
* ``side_effect`` now supports ``before`` and ``after`` keyword
arguments. (Thanks to yardsale8)
* PyPy and PyPy3 are now supported.

The major version change is due to the removal of the ``context`` function.
Replace it with standard ``with`` statement context management:

.. code-block:: python

Don't use context() anymore
file_obj = StringIO()
consume(print(x, file=f) for f in context(file_obj) for x in u'123')

Use a with statement instead
file_obj = StringIO()
with file_obj as f:
consume(print(x, file=f) for x in u'123')

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* New itertools:
* ``adjacent`` and ``groupby_transform`` (Thanks to diazona)
* ``always_iterable`` (Thanks to jaraco)
* (Removed in 3.0.0) ``context`` (Thanks to yardsale8)
* ``divide`` (Thanks to mozbhearsum)
* Improvements to existing itertools:
* ``ilen`` is now slightly faster. (Thanks to wbolster)
* ``peekable`` can now prepend items to an iterable. (Thanks to diazona)

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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)