document changes for YearArchiveView.

    * ``year``: A :class:`~datetime.date` object

      representing the given year.

      .. versionchanged:: 1.5

      Previously, this returned a string.

    * ``next_year``: A :class:`~datetime.date` object

      representing the first day of the next year, according to

      :attr:`~BaseDateListView.allow_empty` and

      :attr:`~DateMixin.allow_future`.

      .. versionadded:: 1.5

    * ``previous_year``: A :class:`~datetime.date` object

      representing the first day of the previous year, according to

      :attr:`~BaseDateListView.allow_empty` and

      :attr:`~DateMixin.allow_future`.

      .. versionadded:: 1.5

    **Notes**

    * Uses a default ``template_name_suffix`` of ``_archive_year``.