v0.2.0

This release mainly adds docs, improves the explanation and API of BitBoard,
and adds Python constructors for important types.

Changelog

• Better docs, especially for BitBoard and the crate root
• Fixed wrong ! operator for CardsSet
• Added CardsSet::remove()
• Added CardsSet constants for all black/red cards
• Added CompactField::all_cards()
• Implemented bitwise ops for BitBoard
• Added BitBoard::insert() and BitBoard::remove()
• Added Python constructor and __repr__() for CompactField
• Added Board::combo_locations_for_card()
• Added Board::from_fields_list() and Python constructor