Graphviz

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Add ``.unflatten()`` method to ``Graph``, ``Digraph``, and ``Source``. Add
standalone ``unflatten()``.

Make ``Source.__str__()`` return the ``.source`` instead of the ``repr()``
(like ``Graph`` and ``Digraph``).

Render with ``dot -K<engine> ...`` instead of ``<engine> ...`` internally
(work around `upstream issue
<https://gitlab.com/graphviz/graphviz/-/issues/1753>`_).

Add documentation hint to archived upstream version for Windows.

Re-render most documentation graphs with Graphviz 2.44.1.

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``Graph`` and ``Digraph`` instances created via the context-manager
returned by ``subgraph()`` now (re)use
``directory``, ``format``, ``engine``, and ``encoding`` from the parent
instead of using defaults (behavioral change).
Note that these attributes are only relevant
when rendering the subgraph independently (i.e. as a stand-alone graph)
from within the ``with``-block, which was previously underdocumented.
PR `116 <https://github.com/xflr6/graphviz/pull/116>`_ BMaxV.
To reflect that the DOT language does not allow subgraph statements
to specify ``strict``
(i.e. no way to override the setting of the containing graph),
instances created via the context-manager are now ``strict=None`` instead of ``False``
(so they continue to render stand-alone as non-strict by default).

Drop Python 3.5 support and tag Python 3.9 support.

Add documentation link to new upstream installation procedure for Windows.

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Adapt ``graphviz.version()`` to support the Graphviz Release version entry
format introduced with ``2.44.2`` (``version()`` is needed to run the tests).

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Document the colon-separated ``node[:port[:compass]]`` format used for
``tail`` and ``head`` points in the ``edge()``- and ``edges()``-methods.
PR `101 <https://github.com/xflr6/graphviz/pull/101>`_ Michał Góral.

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Improve handling of escaped quotes (``\"``). Different from other layout engine
escapes sequences such as ``\l`` and ``\N`` (which are passed on as is by
default), there is no use case for backslash-escaping a literal quote character
because escaping of quotes is done by this library. Therefore, a
backslash-escaped quote (e.g. in ``label='\\"'``) is now treated the same as a
plain unescaped quote, i.e. both ``label='"'`` and ``label='\\"'`` produce
the same DOT source ``[label="\""]`` (a label that renders as a literal quote).
Before this change, use of ``'\\"'`` could break the quoting mechanism creating
invalid or unintended DOT, possibly leading to syntax errors from the rendering
process.

Add notebook section to documentation.

Add ``sphinx.ext.viewcode`` to docs (note that this currently lacks links for
methods, so that not all of the code is linked; use the source repo for reading
on).

Improve test and doc building config.

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Fix missing support for four-part versions in ``graphviz.version()``.