Also doesn't require gil for int and long abs.

Notes:
* I don't think the correct utility code is loaded for complex abs
  (but it should be loaded by the complex data types hopefully)
* Would probably be worth making double and float abs not require gil

Fixed #1647

set.update() is actually variadic.  Fixes #1645.

Add create_extension() hook

Include except clause for PyTuple_SetItem in CPython-Includes

Un-disable Python3-specific slots on pypy3.5

PyPy3: make special dict methods work

The .iterkeys(), .itervalues() and .iteritems() methods are accepted in Cython
even when targetting Python 3.x.  However, this is implemented by a shortcut
inside Optimize.c that is explicitly disabled on PyPy.  This fixes the
situation.

Let IPython magic only import things in `"__all__"`

skip single underscore
minor restructure

IPython magic only import things in `"__all__"`

Make the IPython cell magic only import things in `"__all__"` when `"__all__"` exits.

Fix TODO: how to display this not as code but verbatim?

Pass first arg of visitproc as PyObject*

Pass metaclass as PyObject* (and not PyTypeObject*)

Update language_basics.rst: corrected an example

Correct mistake in doc `early_binding_for_speed.rst`

corrected an example

IPython notebook to Jupyter notebook in docs