Mush

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- Official support for Python 3.

- Drop official support for Windows, although things should still work.

- Move to Travis CI, Read The Docs and Coveralls for development.

- 'How' decorators like :func:`attr` and :func:`item` can now be nested
as well as individually performing nested actions.

- Add :func:`returns` and :meth:`~Runner.add_returning` as new ways to
override the type of a returned value.

- A better pattern for "marker types".

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- Use :obj:`nothing` instead of ``None`` for marker return types,
fixing a bug that occurred when a callable tried to type-map a
result that was ``None``.

- Add an :func:`after` type wrapper for callables that need to wait
until after a resource is used but that can't accept that resource
as a parameter.

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- Allow runners to be instantiated using other runners.

- Allow :meth:`Runner.extend` to be passed :class:`Runner` instances.

- Allow :func:`requires` decorations to be stacked.

- Add a :meth:`Runner.replace` method to aid with testing assembled runners.

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- Initial Release