public Document(string contents)
     : this()
 {
     IRevision intialRevision = new InitialRevision(contents);
     CurrentRevision = intialRevision;
     _revisionMap.Add(intialRevision.Id, Tuple.Create(intialRevision, RevisionStatus.Applied));
 }
 public Document()
 {
     CurrentRevision = new InitialRevision();
     Subcribers = new List<Subscriber>();
 }