Concepts

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Add ``load()`` inferring the format form the file suffix.

Tag Python 3.7 support, add simple tox config.

Fix collections.MutableSet PendingDeprecationWarning.

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Increase API docs coverage.

Use compatible release version specifiers (bump ``graphviz`` to ~=0.7).

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Drop Python 3.3 support.

Include LICENSE file in wheel.

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Port most tests from nose/unittest to pytest, add Travis CI and coveralls.

Update package meta data, tag python 3.6 support.

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Let the ``.graphviz()``-method pass ``kwargs`` to the returned graph (e.g. ``format='png'``).

Relax optional ``graphivz`` dependency to < 1.0.

Added extended Sphinx-based documentation.

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Added ``move_object()`` and ``move_property()`` to definitions.

The ``take()``-method of definitions now supports skipping all objects or properties
when called with empty iterables (default None means include all).

Simplified ``__getitem__`` examples.