Use Py_ssize_t for length arguments of PyArg_ParseTuple

This API was introduced in Python 2.5 and the old one (using ints) has
been deprecated since Python 3.8.

See #108.

This API was introduced in Python 2.5 and the old one (using ints) has
been deprecated since Python 3.8.

Fixes #108.

Require CFFI on CPython for pure-Python operation.

Fixes #77

Allow sweeping cache without cache_size and with cache_size_bytes only.

This reverts commit e6d183b1.

Fully test the C implementation of the PickleCache

Fix discrepancies between it and the Python implementation:

  - The C implementation now raises ``ValueError`` instead of
    ``AssertionError`` for certain types of bad inputs.
  - The Python implementation uses the C wording for error messages.
  - The C implementation properly implements ``IPickleCache``; methods
    unique to the Python implementation were moved to
    ``IExtendedPickleCache``.
  - The Python implementation raises ``AttributeError`` if a
    persistent class doesn't have a ``p_jar`` attribute.

Fixes #102

Exclude the 'terryfy' directory from wheels and sdists

Always format 8-byte oids as ints in hexadecimal.

Fixes #99

Fixes #95

Built on #97 as they touch the same code.

Fix the repr of the persistent objects to include the module name when
using the C extension. This matches the pure-Python behaviour and the
behaviour prior to 4.4.0.

Fixes #92

Explicitly use unsigned hex literals when [un]packing timestamps.

This should fix #86

Run a compiler with wrapv turned off to verify this.

Make test pass when run with 'tox'

I used to get failures like

    py27 runtests: commands[0] | zope-testrunner --test-path=.
    Test-module import failures:

    Module: persistent.tests.test_docs

    IOError: [Errno 2] No such file or directory: '/home/mg/src/zopefoundation/persistent/.tox/docs/api/cache.rst'

    Running zope.testrunner.layer.UnitTests tests:
      Set up zope.testrunner.layer.UnitTests in 0.000 seconds.
      Ran 524 tests with 0 failures, 1 errors and 0 skipped in 0.249 seconds.
    Tearing down left over layers:
      Tear down zope.testrunner.layer.UnitTests in 0.000 seconds.

    Test-modules with import problems:
      persistent.tests.test_docs
    ERROR: InvocationError for command '/home/mg/src/zopefoundation/persistent/.tox/py27/bin/zope-testrunner --test-path=.' (exited with code 1)

because adding a ../ at the end of the path is not the same as stripping
off the last path component when symlinks are involved!

    $ cd .tox && ./py27/bin/python
    >>> >>> from persistent.tests.test_docs import __file__
    >>> __file__
    '/home/mg/src/zopefoundation/persistent/.tox/py27/local/lib/python2.7/site-packages/persistent/tests/test_docs.pyc'

.tox/py27/local/lib is a symlink to /home/mg/src/zopefoundation/persistent/.tox/py27/lib
and so .tox/py27/local/lib/.. is pointing to .tox/py27, while
os.path.abspath() thinks it's pointing to .tox/py27/local.

    >>> import os
    >>> here = os.path.dirname(__file__)
    >>> while not os.path.exists(os.path.join(here, 'setup.py')): here = os.path.join(here, '..')
    ...
    >>> here
    '/home/mg/src/zopefoundation/persistent/.tox/py27/local/lib/python2.7/site-packages/persistent/tests/../../../../../../..'
    >>> os.path.abspath(here)
    '/home/mg/src/zopefoundation/persistent/.tox'
    >>> os.path.exists(os.path.join(here, 'setup.py'))
    True
    >>> os.path.exists(os.path.join(os.path.abspath(here), 'setup.py'))
    False
    >>> os.path.exists(os.path.abspath(os.path.join(here, 'setup.py')))
    False

Fix wheel building for PyPy.

Don't confuse ext_modules with headers.

Fixes #88