Log Message:
Update to 0.18.0. From the changelog:

ship accumulated bugfixes and catchup with wayback machine changes.

special thanks to Paul Wise for the immesurable patience on
the wayback plugin and test suite, and to Jelmer Vernooij for the
Debian Janitor.

New features:

* Add support for saving page resources to the Wayback Machine too,
  thanks Paul Wise!

API changes:

* we now generate a standard message-id, which has brackets around it

Bugfixes:

* fix rare crash in feed2exec parse with an empty `mailbox` setting
* fix feedparser dependencies for newer python
* catchup with html2text again (2020.1.16)
* add failing test and fix for cachecontrol 0.12.10 new API (Closes: GL#22)
* do not cache requests in plugins (Closes: #1001412, GL#26)
* Require feedparser 5 as minimum version for Python 3, thanks Paul Wise

Documentation:

* mention (lack of) Gemini and other protocol support
* leave Freenode for oftc.net

Cleanup, CI, linting:

* avoid dateparser bug workaround in newer versions
* drop support for python 3.5, add 3.9
* enforce black in tox, but not in CI
* first pass at type checking with mypy, with failures allowed
* switch to setup.cfg as much as possible
* fix rst syntax since we are not hacking it anymore
* mention build module, which may be necessary for newer setuptools_scm
* move fixtures to conftest.py
* use pytest.mark.network instead of xfail