Gocept-month

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- Migrate repository to https://bitbucket.org/gocept/gocept.month

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- Add placeholder for month widget in z3c forms describing the required month
format.

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- Split off widgets into setuptools extra ``form``, and don't include the
``browser`` ZCML by ourselves, so clients can use only the domain part of
this package without the UI parts.

- Added ``firstOfMonth`` method to ``Month``.

- Using `zope.formlib >= 4.0` instead of `zope.app.form`.

- Updated to ZTK 1.1.5.

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- Add MonthInterval.forYear().
- Declared ``fromString`` method as a class method in interface.

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- Added ``__contains__`` method on ``Month``.

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- Declare dependencies that some upstream packages need but don't declare.

- Use stdlib's doctest module, not zope.testing's which is deprecated.