Comparator

------------------

- BREAKING - All ``source`` modules and methods have been stripped out
- Functionality has been moved to the ``spackl`` package (``pip install spackl``)
- The ``comparator`` package will expect ``spackl`` to be used for all ``left`` and ``right`` data sources

---------------------

- Adds better transaction handling in the PostgresDb class
- Cleans up calls to connect() in the Db classes

---------------------

- BREAKING - ``QueryPair`` arguments order has changed (``QueryPair(left, lquery, right, rquery)``)
- ``QueryPair``, ``Comparator``, and ``ComparatorSet`` no longer require a "right" Db

---------------------

- DEPRECATED - the ``from_list`` method on ``ComparatorSet``
- adds the ``QueryPair`` class
- BREAKING - ``Comparator`` and ``ComparatorSet`` are instantiated with ``QueryPair`` objects
- BREAKING - ``ComparatorSet.from_dict()`` requires the dict as the first argument
- BREAKING - ``QueryResult.keys()`` and ``QueryResult.values()`` both return generators
- the ``rquery`` passed to a ``QueryPair`` can be formatted with the ``lquery`` query result
- adds the ``QueryResultCol`` class
- adds the ``append``, ``pop``, ``extend``, and ``filter`` methods on ``QueryResult``
- downgrades pandas version requirement to >=0.22.0
- improves docstrings on ``QueryResult`` methods
- adds slice handling to ``QueryResult``
- adds ``empty`` property to ``QueryResult``

------------------

- adds MANIFEST.in for readme and changes

------------------

- adds ``creds_file`` to possible BigQueryDb init kwargs