code: public static Vertex newB()
      {
          return new Vertex(Predefine.TAG_BIGIN, " ", new CoreDictionary.Attribute(Nature.begin, Predefine.MAX_FREQUENCY / 10), CoreDictionary.getWordID(Predefine.TAG_BIGIN));
      }
docs: 生成线程安全的起始节点
  @return