Hypatia

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- XXX

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- Drop (unreleased) support for Python 3.3 and Python 3.4 (the ``persistent``
package no longer supports these versions).

- Drop (unreleased) support for Python 3.5 (too difficult to build correctly --
even with pyenv -- to bother).

- Drop (released) support for Python 2.6 and 3.2.

- Add support for Python 3.6, 3.7, 3.8, 3.9, 3.10 (thanks to Thierry Florac).

- Use pytest instead of python setup.py test -q in tox.ini.

- Change how cross-version coverage is computed in tests.

- Remove unused hypatia/text/ricecode.py file.

- Change building of docs slightly to cope with modified github protocols.
Some warnings are unearthed with newer Sphinx, which I've not
caught by turning warnings into errors yet, because I don't understand them.

- Don't modify queries attribute when optimizing And or Or, return a new
instance instead. This change is needed to open new optimization
possibilities, like factorization.

- Fix Comparator __eq__ method to include type in comparison,
previously NotAny('index', [1]) was equal to Any('index', [1]) for example.

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- Depend on the ``ZODB`` package rather than the ``ZODB3`` package. The former
is a newer ZODB packaging, implying ZODB4. If you actually require ZODB v3,
you will need to pin ``hypatia`` to an older release. You should know that
the most recent release of ``ZODB3`` at this time (3.11) actually implies
ZODB v4 (I know it's not exactly obvious, but Jim ensures me it is), so if
you really require ZODB v3, you'll need to pin ``ZODB3`` to below 3.11 and
``hypatia`` to below this release.

- Keyword indices now have a ``unique_values`` method like Field indexes.

- Calling ``hypatia.util.ResultSet.first()`` and
``hypatia.util.ResultSet.one()`` is now idempotent. Calling it a second time
will return the same value, and calling it will not effect the result set's
iterability (it will start from zero).

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- Query objects are now consulted for intersect and union operations via
methods, instead of the intersection/union logic being embedded in And and Or
query objects. This makes it possible to create query object types which
intersect and/or union differently when combined with other query results.

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- Fix a typo in the Sphinx docs, which causes intersphinx references to
fail.

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- Add a ``unique_values`` API to field index.

- Sometimes an ``index`` attribute could not be found to resolve a result
set when deeply nesting boolean operations (like And and Or). See
https://github.com/Pylons/hypatia/pull/5

- Throw an Unsortable properly when a field index without any docids is used as
a sort index and ``raise_unsortable`` is ``True``.