Add int docstring template to class init.

def _int_doc(cls):
    """Add int docstring template to class init."""
    def __init__(self, value=None, **kwargs):
        if value is not None:
            kwargs['value'] = value
        super(cls, self).__init__(**kwargs)

    __init__.__doc__ = _int_doc_t
    cls.__init__ = __init__
    return cls