Mailinglogger

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- Drop Python 2 support.

- Add TLS support.

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- Python 3.8 support.

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- Python 3 support

- Renaming the modules within the ``mailinglogger`` package to have
sane capitalisation.

Thanks to Max Shepherd for breaking the back of the Python 3 work.

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- Drop Zope and Plone support

- Drop ZConfig support

- Removed the deprecated ``ignore`` parameter to
:class:`MailingLogger` and :class:`SummarisingLogger`.
Use `filter objects`__ instead.

__ http://docs.python.org/library/logging.html#filter-objects

- Move from ``zope.testrunner`` to `pytest`__ for running tests.

__ https://docs.pytest.org/en/latest/

- Switch from `manuel`__ to `sybil`__ for checking examples in
documentation.

__ http://packages.python.org/manuel/

__ http://sybil.readthedocs.io/en/latest/

- Moved from buildout to virtualenv for development.

- Gracefully handle bugs elsewhere that call :meth:`SummarisingLogger.close`
more than once in a multi-threaded or multi-process environment.

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- Implemented flood limiting in :class:`SummarisingLogger` to prevent
overly large emails being sent.

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- Added the ability to wrap the body of emails sent in a template.

- Added documentation and tools for the sending of HTML emails.

- Fixed a bug that resulted in a unicode error when sending emails
after a unicode message was logged.