v6.1.0

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* fix #587: don't fail file finders when distribution is not given
* fix #524: new parameters ``normalize`` and ``version_cls`` to customize the version normalization class.
* fix #585: switch from toml to tomli for toml 1.0 support
* fix #591: allow to opt in for searching parent directories in the api
* fix #589: handle yaml encoding using the expected defaults
* fix #575: recommend storing the version_module inside of ``mypkg/_version.py``
* fix #571: accept branches starting with ``v`` as release branches
* fix #557: Use ``packaging.version`` for ``version_tuple``
* fix #544: enhance errors on unsupported python/setuptools versions