Graphviz

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Add low-level functions ``render()``, ``pipe()``, and ``view()`` for directly working with
existing files and strings.

Support all ``render()``-arguments in the ``view()``-short-cut-method.

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Added ``'patchwork'`` engine.

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Add support for ``strict`` graphs and digraphs.

Hide ``render/pipe()`` subprocess console window on Windows when invoked from
non-console process (e.g. from IDLE).

Improve documentation markup/wording.

Make ``TestNoent`` more robust.

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Make ``_repr_svg_()`` available on ``Source`` (pull request RafalSkolasinski).

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Fixed ``view()``-method on Linux under Python 3 (pull request Antony Lee).

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Fixed ``view()``-method on Linux and Darwin (pull request Eric L. Frederich).