code: public MDAGNode addOutgoingTransition(char letter, boolean targetAcceptStateStatus)
      {
          MDAGNode newTargetNode = new MDAGNode(targetAcceptStateStatus);
          newTargetNode.incomingTransitionCount++;
          
          outgoingTransitionTreeMap.put(letter, newTargetNode);
          return newTargetNode;
      }
docs: 新建一个转移目标<br>
  Creates an outgoing _transition labeled with a
  given char that has a new node as its target.
  
  @param letter                        a char representing the desired label of the _transition
  @param targetAcceptStateStatus       a boolean representing to-be-created _transition target node's accept status
  @return                              the (newly created) MDAGNode that is the target of the created _transition