0.2.0

• Remove unused RankingsDatabase classes and conversion functions.
• Add CisTargetDatabase class for reading rankings/scores for regions/genes from a cisTarget scores or rankings database (only Feather v2 format), which requires pyarrow >= 8.0.0 instead of <=0.17.1 needed for the old FeatherRankingDatabase class.
• Update FeatherRankingDatabase to use CisTargetDatabase to read cisTarget databases.
• Reformat code and update type annotations.