Feincms3-meta

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- Switched to a declarative setup.
- Switched from Travis CI to GitHub actions.
- Changed the HTML generation to preserve single quotes etc. in Open Graph tags
when it is safe to do so.
- Raised the minimum requirement to Python >= 3.8, Django >= 3.2.
- Added a unittest verifying that blank strings are skipped.
- Removed the strange whitespace between tags.

~~~~~~~~~~~~~~~~~~~

- Reinstated the support for ``og:site_name`` which was lost in the
rework leading to 2.0.
- Added a `django-imagefield
<https://github.com/matthiask/django-imagefield>`__ dependency which
allows us to provide OpenGraph images in the best format.

~~~~~~~~~~~~~~~~~~~

- Reworked the internals of the utils module and made the API surface
smaller.
- Added back support for the ``og:image:width`` and ``og:image:height``
tags.

~~~~~~~~~~~~~~~~~~~

- Changed the meta tags dictionary to also build absolute URIs when
calling ``update()`` after the ``meta_tags`` helper returns.
- Changed ``meta_tags`` to no longer produce a ``<meta
name="description" content="">`` tag if the description is empty.
- Switched the preferred quote to ``"`` and started using `black
<https://pypi.org/project/black/>`_ to automatically format Python
code.
- Removed the deprecated ``meta_tags_html`` function.
- Added new fields for overriding the author and robots meta tags.

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- Added the possibility to override values from ``META_TAGS`` using an
additional ``defaults`` argument to ``meta_tags``.
- Converted the tests to the same structure the other feincms3 packages
use, added a tox-based test and style checks while doing that.
- Increased test coverage.

~~~~~~~~~~~~~~~~~~~

- Made the return value of ``meta_tags`` a subclass of ``dict`` which
renders meta tags as HTML.
- Added a deprecation warning to ``meta_tags_html``.