Dataflake.docbuilder

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- Drop support for documentation generated with ``z3c.recipe.sphinx``.

- Drop support for Subversion and Mercurial.

- Drop option ``copy-output``. Always copy HTML output to HTML output folder.

- Add support for Python 3.8, 3.9, 3.10, 3.11.

- Drop support for Python 2.7, 3.5, 3.6.

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- make sure to convert shell output to unicode on Python 3 and 2.
- before invoking ``setup.py`` commands in a subshell, make sure
it is present.

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- add option ``-n`` to skip checkout and build of software packages

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- test and declare support for Python 3.7

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- use pkgutil-style namespace declaration
- package cleanup (``.gitignore``, ``MANIFEST.in``, ``README.rst``)
- docs cleanup (``Makefile``, ``conf.py``)
- tests cleanup (``tox.ini``)
- remove unsupported documentation bits

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- Python 3 compatibility