0.8.15

Added support for loading containers into specialized VisiData Sheet and IndexSheet subclasses; added to_visidata() exporter to all containers.

Added StyleConfig class for configuring display characteristics. Added default StyleConfigCSS for improved default HTML presentation.

Added Series.rank_ordinal, Series.rank_dense, Series.rank_mean, Series.rank_min, Series.rank_max.

Added Frame.rank_ordinal, Frame.rank_dense, Frame.rank_mean, Frame.rank_min, Frame.rank_max.

Fixed issue in Series.from_element() and Frame.from_element() that would broadcast some iterables instead of treat them as an element.

Extended Frame.unset_index() to support unsetting IndexHierarchy.