Graphviz

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Add ``clear()``-method for ``Graph`` and ``Digraph``.

Add ``grapviz.version()`` function.

Drop dot source extra indent for edge statements following dotguide examples.

Include LICENSE file in wheel.

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Fix ``TypeError`` in ``graphviz.pipe()`` with invalid dot code under Python 3.

Add ``copy()``-method for ``Graph``, ``Digraph``, and ``Source``.

Add ``graphviz.render(..., quiet=True)``.

Fix ``graphivz.view()`` exception on unsupported platform.

Raise a dedicated ``RuntimeError`` subclass ``graphviz.ExecutableNotFound`` when the
Graphviz executables are not found.

Port tests from ``nose/unittest`` to ``pytest``, extend, use mocks.

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Support setting top-level attrs with ``g.attr(key=value)``.

Add context manager usage of ``subgraph()`` for adding a subgraph in a with-block.

Add json-based output formats to known ``FORMATS`` (Graphviz 2.40+).

Drop extra indent level for DOT source with nonempty ``graph/node/edge_attr``.

Add a final newline to a saved DOT source file if it does not end with one.

Raise ``subprocess.CalledProcessError`` on non-zero exit status from rendering.

Raise early when adding a ``subgraph()`` with ``strict=True`` (avoid DOT syntax error).

Make undocumented ``quote()``, ``quote_edge()``, and ``attributes()`` methods private.

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Drop Python 2.6 support (use ``graphviz<0.6`` there).

Improve tests for ``mkdirs()``.

Better document adding custom DOT using the ``body`` attribute.

Add ``view()``-support for FreeBSD (pull request Julien Gamba).

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Add ``ENGINES`` and ``FORMATS`` to the documented public API.

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Fixed PY3 compatibility.