参考
https://zhuanlan.zhihu.com/p/62486641
https://zhuanlan.zhihu.com/p/88376673
https://github.com/zy1996code/nlp_basic_model/blob/master/lstm_attention.py
https://www.jianshu.com/p/0d1e9f0db887
https://blog.csdn.net/uhauha2929/article/details/81951760