2022-12-24: added get_key_value and peek_key_value, tagged 0.3.2
2022-12-24: added mru/resize/clear, tagged 0.3.1
2022-12-24: added push/pop/lru, fix order bug, tagged 0.3.0
2022-12-17: added peek method, tagged 0.2.1
2022-12-11: added capacity method, tagged 0.2.0
2020-01-05: initial release, tagged 0.1.0