Grokcore.annotation

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- Add LazyAnnotation and LazyAnnotationProperty.

- Drop support of Python 2.6 and claim support for Python 3.4, 3.5, 3.6 and PyPy.

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- Update tests.

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- Updating MANIFEST.in, fixing a brown paper bag release.

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- Add ``queryAnnotation()`` to return an annotation. Return None if it
doesn't exists. This helper will never do any write operation in the
database.

- Add ``deleteAnnotation()`` to delete an annotation (if it exists).

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- Use ``provideAdapter()`` from grokcore.component.util.

- Made package comply to zope.org repository policy.

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* Use zope.container instead of zope.app.container.