code: public static final Nature create(String name)
      {
          Nature nature = fromString(name);
          if (nature == null)
              return new Nature(name);
          return nature;
      }
docs: 创建自定义词性,如果已有该对应词性,则直接返回已有的词性
  
  @param name 字符串词性
  @return Enum词性