Log Message:
py-vdirsyncer: update to 0.19.0.

Version 0.19.0
==============

- Add "shell" password fetch strategy to pass command string to a shell.
- Add "description" and "order" as metadata.  These fetch \ 
the CalDAV:
  calendar-description, ``CardDAV:addressbook-description`` and
  ``apple-ns:calendar-order`` properties respectively.
- Add a new ``showconfig`` status. This prints *some* configuration values as
  JSON. This is intended to be used by external tools and helpers that interact
  with ``vdirsyncer``, and considered experimental.
- Update TLS-related tests that were failing due to weak MDs. :gh:`903`
- ``pytest-httpserver`` and ``trustme`` are now required for tests.
- ``pytest-localserver`` is no longer required for tests.
- Multithreaded support has been dropped. The ``"--max-workers`` has been \ 
removed.
- A new ``asyncio`` backend is now used. So far, this shows substantial speed
  improvements in ``discovery`` and ``metasync``, but little change in `sync`.
  This will likely continue improving over time. :gh:`906`
- The ``google`` storage types no longer require ``requests-oauthlib``, but
  require ``python-aiohttp-oauthlib`` instead.
- Vdirsyncer no longer includes experimental support for `EteSync
  <https://www.etesync.com/>`_. The existing integration had not been supported
  for a long time and no longer worked. Support for external storages may be
  added if anyone is interested in maintaining an EteSync plugin. EteSync
  users should consider using `etesync-dav`_.
- The ``plist`` for macOS has been dropped. It was broken and homebrew
  generates their own based on package metadata. macOS users are encouraged to
  use that as a reference.

.. _etesync-dav: https://github.com/etesync/etesync-dav

Changes to SSL configuration
----------------------------

Support for ``md5`` and ``sha1`` certificate fingerprints has been dropped. If
you're validating certificate fingerprints, use ``sha256`` instead.

When using a custom ``verify_fingerprint``, CA validation is always disabled.

If ``verify_fingerprint`` is unset, CA verification is always active. Disabling
both features is insecure and no longer supported.

The ``verify`` parameter no longer takes boolean values, it is now optional and
only takes a string to a custom CA for verification.

The ``verify`` and ``verify_fingerprint`` will likely be merged into a single
parameter in future.