Repair incorrect C-API signature usage for PyUnicode_DecodeUTF16() when optimising bytes decoding from UTF-16(LE/BE)

Closes #1696

Remove obsolete documentation

Fix bad indentation in a pyximport test

The indentation was inadvertently broken when expanding tabs in
e908c0b9.

Fixes:

    $ python pyximport/test/test_reload.py
      File "pyximport/test/test_reload.py", line 23
        assert hello.x == 1
        ^
    IndentationError: unexpected indent

Fix incorrect use of flags in re.sub()

The 4th argument of re.sub() is maximum number of substitutions, not
flags.

re.M affects only semantics of ^ and $, so it wouldn't have any effect
on this regexp.

Update language_basics.rst

Allow "cdef inline" with default values in .pxd

Add declarations for several PyLong_Type functions

Add declaration for PyImport_ImportModuleLevel

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