Bitsets

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Added ``reverse`` argument to ``.atoms()`` and ``.inatoms()``, improved visualization edge order.

Changed series ``frombitsets`` argument to iterable argument instead of ``*args``, fixed bits method.

Improved doctests.

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Some cleanup.

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Added ``.atoms()`` and ``.inatoms()`` method.

Backwards incompatible: renamed ``from_spam`` methods to ``fromspam``.

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Add ``reduce_and``, ``reduce_or`` on series and as class-only methods on all bitsets.

Improved visualization using ``graphviz`` 0.2 with new api.

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Added visualization.

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Added ``.all()`` and ``.any()`` methods, improved ``__nonzero__``.

Improved documentation.