public Task <long> AppendToStreamAsync(string streamName, params EventData[] events)
 => AppendToStreamAsync(
     streamName,
     Concurrency.Ignore(),
     events);
 public Task <long> AppendToStreamAsync(string streamName, long version, params EventData[] events)
 => AppendToStreamAsync(
     streamName,
     Concurrency.Match(version),
     events);