Performance enhancements to ``Index`` initialization.
Performance enhancements to ``Series.iter_element().apply()``, ``Series.iter_element().map_any()``, ``Series.iter_element().map_all()``, and ``Series.iter_element().map_fill()``.
Performance enhancements to ``Frame.iter_series().apply()``, ``Frame.iter_tuple().apply()``, ``Frame.iter_array().apply()``.