Malaffinity

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* Move test dependencies to ``extras_require`` in setup.py, and have
``tests_require`` mirror that.
* Add documentation dependencies to ``extras_require`` in setup.py.
* Make all docstrings PEP 257 compliant.
* Add more classifiers to ``setup.py``.

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* Have Travis deploy the package to PyPI when a release is drafted.

This release exists solely to test that the above is working.
No code changes have been made.

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* Fix tests up to use the ``mock`` module, and be less hacky.
* Hook tests up to ``setup.py``, so ``python setup.py test`` can be called,
for the test suite to run.
* Add version constraints in for dependencies.

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* Create the ``comparison`` method, and have ``calculate_affinity`` use that
to retrieve both sets of scores.
* Rewrite the docstrings in the ``MALAffinity`` class, to be more useful and
more compliant with le Sphinx syntax.
* Add docs to the project, and have them hosted on readthedocs.io.
* Add (badly written) tests, and hook them up to Travis and Coveralls.
* Get rid of Markdown altogether, and rewrite the README, as most of the info
is now in the docs.

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* Fix a typo in the ``calcs.pearson`` docstring, which incorrectly said
the ``:rtype`` was a bool.
* Use the ``find_all`` BS4 method instead of ``findAll``.
* Fix a typo in the "Shared rated anime count is less than required" exception
message, which incorrectly stated that the minimum required was ten, when it's
actually eleven.
* Add a docstring for ``.__about__``.
* Add a docstring for ``MALAffinity._retrieve_scores``.
* Remove the useless kwargs from ``MALAffinity._retrieve_scores``.
* Make the ``statistics`` pypi package a requirement for all Python versions.
* Add a ``__repr__`` to the ``MALAffinity`` class.
* Move the ``_retrieve_scores`` method in the ``MALAffinity`` class
to its own file (``endpoints.py``).
* Create a ``const.py`` file for constants.
* Add a `` NOQA`` comment to the ``.__about__`` imports in ``__init__``, to suppress
the F401 flake8 warnings.

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* Move the MALAffinity class to its own separate file (``malaffinity.malaffinity``)
and import that into the ``malaffinity`` namespace via ``__init__``.
* Move exceptions to its own separate file (``malaffinity.exceptions``).
* Modify description of the package slightly ("Calculate affinity between
**two** MyAnimeList users" => "Calculate affinity between MyAnimeList users").
* Add exception message for when the standard deviation of one of the two users'
scores is zero, and affinity can't be calculated.
* Create the base ``MALAffinityException`` class and derive all malaffinity
exceptions from that.
* Add docstrings for ``malaffinity.calcs``.
* Modify docstrings to remove typos and unnecessary information,
and reword some sections.
* Reword exception messages to be more useful.
* Have the ``init`` method return ``self``, to allow for
`chaining <https://en.wikipedia.org/wiki/Method_chaining>`__.
* Make all code PEP8-compliant (ignoring F401 for meta reasons).