API change: ``IndexHierarchy`` numerical and statistical methods, such as ``sum()``, ``var()``, ``std()``, ``cumprod()``, ``cumsum()``, now raise ``NotImplementedError``.
API change: ``Frame.astype[]`` calls now set ``consolidate_blocks`` to ``False`` by default.
API change: ``composite_index`` and ``composite_index_fill_value`` parameters removed from ``Frame.join_left``, ``Frame.join_right``, ``Frame.join_inner``, and ``Frame.join_outer``; added ``include_index`` parameter.
API change: ``IndexDefaultFactory`` renamed ``IndexDefaultConstructorFactory``.
Added ``via_dt.year_month``.