Z3c.checkversions

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- Python 3 support by Nicolas Dietrich (`GH 2`_, `GH 4`_)

.. _GH 2: https://github.com/zopefoundation/z3c.checkversions/pull/2
.. _GH 4: https://github.com/zopefoundation/z3c.checkversions/pull/4

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- ignore installed packages while searching for new versions, only look in
the package index (makes the test suite more reliable, among other things).
- fix IndexError: list index out of range when buildout.cfg had a package with
a blank version pin.
- show updates for non-final package versions, if there's a newer non-final
version available on PyPI (`GH 1`_)

.. _GH 1: https://github.com/zopefoundation/z3c.checkversions/pull/1

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- fixed edge case bug where 1.0 was never updated to 1.0.x
- warn buildout users about the extra requirement

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- added a `blacklist` option for passing versions to avoid
(possibly coming from a buildbot)
- added a `incremental` option to suggest only one upgrade
- remove a temporary file during tests

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- don't accumulate old comments
- prefer final versions

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- added a verbose option to print old versions as well
- updated metadata, doc and license