--------------------------
* Changed: add arguments ``num_workers`` and ``verbose`` to
``audformat.Database.drop_files()``,
``audformat.Database.map_files()``,
``audformat.Database.pick_files()``,
``audformat.Database.save()``
* Changed: ``audformat.segmented_index()``
support ``int`` and ``float``, which will be interpreted as seconds
* Fixed: ``audformat.utils.to_segmented_index()``
returns correct index type for ``NaT``