Static-frame

Added ``Frame.cov``, ``Series.cov``, and ``Batch.cov``.

Performance enhancements to ``loc`` selections by element.

Implemented support for multiprocessing Frame writing from ``StoreZip`` subclasses used by ``Bus``, ``Batch``, and ``Quilt``.

Enabled ``write_max_workers`` and ``write_chunksize`` in ``StoreConfig``.

Added py.typed file to package.

Improved exceptions raised when attempting to write to a file at an invalid path.

Improved handling of reading files with columns but no data with ``Frame.from_delimited``.

Frame.rename`` now accepts optional arguments for ``index`` and ``columns`` renaming.

``Series.rename`` now accepts an optional argument for ``index`` renaming.

Added ``Frame.relabel_shift_in()`` and ``Frame.relabel_shift_out()``.

Fixed issue where ``Frame.dropna()`` fails on single-columns ``Frame``.

Extended ``IndexHierarchy.level_drop`` to perform corresponding drops on ``name`` when ``name`` is an appropriately sized tuple.

Extended ``Frame.set_index`` to support creating a 1D index of tuples when more than one column is selected.

Frame.from_sql`` now properly applies ``dtypes`` to columns used by ``index_depth`` selections.

Added ``Index.unique`` and ``IndexHierarchy.unique``, both taking a ``depth_level`` specifier for selecting one or more depths.

Fixed issue with ``Frame.bloc`` selections that result in a zero-sized ``Series``.

Refined ``Frame.bloc`` selections to reduce type coercion.

Improved ``Frame.assign.bloc`` when assigning with ``Series`` and ``Frame``.

Added ``iloc_searchsorted()`` and ``loc_searchsorted()`` to ``Index``, ``IndexDatetime``, and ``IndexHierarchy``.

Added ``ddof`` parameter to all containers that expose ``std`` and ``var``.

Fixed issue with ``Frame.assign`` where there was a dependency on the order of column labels given in selection.

Improved handling for NumPy Boolean types stored in SQLite DBs via ``StoreSQLite`` interfaces.

Improved `loc_to_iloc()` methods to raise for missing keys in `Index` created where `loc_is_iloc`.