Update cffi to 1.12.0

[pyup-bot]

This PR updates cffi from 1.11.5 to 1.12.0.

Changelog

1.12

=====

* `Direct support for pkg-config`__.

* ``ffi.from_buffer()`` takes a new optional *first* argument that gives
the array type of the result.  It also takes an optional keyword argument
``require_writable`` to refuse read-only Python buffers.

* ``ffi.new()``, ``ffi.gc()`` or ``ffi.from_buffer()`` cdata objects
can now be released at known times, either by using the ``with``
keyword or by calling the new ``ffi.release()``.

* Windows, CPython 3.x: cffi modules are linked with ``python3.dll``
again.  This makes them independant on the exact CPython version,
like they are on other platforms.  **It requires virtualenv 16.0.0.**

* Accept an expression like ``ffi.new("int[4]", p)`` if ``p`` is itself
another cdata ``int[4]``.

* CPython 2.x: ``ffi.dlopen()`` failed with non-ascii file names on Posix

* CPython: if a thread is started from C and then runs Python code (with
callbacks or with the embedding solution), then previous versions of
cffi would contain possible crashes and/or memory leaks.  Hopefully,
this has been fixed (see `issue 362`_).

* Support for ``ffi.cdef(..., pack=N)`` where N is a power of two.
Means to emulate ``pragma pack(N)`` on MSVC.  Also, the default on
Windows is now ``pack=8``, like on MSVC.  This might make a difference
in corner cases, although I can't think of one in the context of CFFI.
The old way ``ffi.cdef(..., packed=True)`` remains and is equivalent
to ``pack=1`` (saying e.g. that fields like ``int`` should be aligned
to 1 byte instead of 4).

.. __: cdef.htmlpkgconfig
.. _`issue 362`: https://bitbucket.org/cffi/cffi/issues/362/


Older Versions
==============

Links

• PyPI: https://pypi.org/project/cffi
• Changelog: https://pyup.io/changelogs/cffi/
• Docs: http://cffi.readthedocs.org