Add support for Python 3.7

* [532](https://github.com/stripe/stripe-python/pull/532) Add support for subscription schedules

=========================

Bug Fixes
---------

- `2895 <https://github.com/pytest-dev/pytest/issues/2895>`_: The ``pytest_report_collectionfinish`` hook now is also called with ``--collect-only``.


- `3899 <https://github.com/pytest-dev/pytest/issues/3899>`_: Do not raise ``UsageError`` when an imported package has a ``pytest_plugins.py`` child module.


- `4347 <https://github.com/pytest-dev/pytest/issues/4347>`_: Fix output capturing when using pdb++ with recursive debugging.


- `4592 <https://github.com/pytest-dev/pytest/issues/4592>`_: Fix handling of ``collect_ignore`` via parent ``conftest.py``.


- `4700 <https://github.com/pytest-dev/pytest/issues/4700>`_: Fix regression where ``setUpClass`` would always be called in subclasses even if all tests
were skipped by a ``unittest.skip()`` decorator applied in the subclass.


- `4739 <https://github.com/pytest-dev/pytest/issues/4739>`_: Fix ``parametrize(... ids=<function>)`` when the function returns non-strings.


- `4745 <https://github.com/pytest-dev/pytest/issues/4745>`_: Fix/improve collection of args when passing in ``__init__.py`` and a test file.


- `4770 <https://github.com/pytest-dev/pytest/issues/4770>`_: ``more_itertools`` is now constrained to <6.0.0 when required for Python 2.7 compatibility.


- `526 <https://github.com/pytest-dev/pytest/issues/526>`_: Fix "ValueError: Plugin already registered" exceptions when running in build directories that symlink to actual source.



Improved Documentation
----------------------

- `3899 <https://github.com/pytest-dev/pytest/issues/3899>`_: Add note to ``plugins.rst`` that ``pytest_plugins`` should not be used as a name for a user module containing plugins.


- `4324 <https://github.com/pytest-dev/pytest/issues/4324>`_: Document how to use ``raises`` and ``does_not_raise`` to write parametrized tests with conditional raises.


- `4709 <https://github.com/pytest-dev/pytest/issues/4709>`_: Document how to customize test failure messages when using
``pytest.warns``.



Trivial/Internal Changes
------------------------

- `4741 <https://github.com/pytest-dev/pytest/issues/4741>`_: Some verbosity related attributes of the TerminalReporter plugin are now
read only properties.