NewMemoryStorage creates an empty memoryStorage.

ErrCompacted is returned by Storage.Entries/Compact when a requested index is unavailable because it predates the last snapshot.

ErrSnapOutOfDate is returned by Storage.CreateSnapshot when a requested index is older than the existing snapshot.

ErrSnapshotTemporarilyUnavailable is returned by the Storage interface when the required snapshot is temporarily unavailable.

ErrUnavailable is returned by Storage interface when the requested log entries are unavailable.

Storage is an interface that may be implemented by the application to retrieve log entries from storage.