StatusStorage::Memory: automatic save and load are now disabled. Those were confusing and did no good.
App::BusyBird::StatusStorage: change the spec of ack_statuses(). It is now a sequential ack instead of selective ack. Sequential ack is enough for typical use cases. If selective ack is necessary, one can use get_statuses and put_statuses (although, this is less efficient..)
Test::BusyBird::StatusStorage: fix test_storage_common() in accordance to the spec change in ack_statuses().
Test::BusyBird::StatusStorage: fix test_storage_truncation() in accordance to the spec change in ack_statuses(). Add reminder to add more tests in test_storage_ordered().