seq2seq 方面比较简洁的教程，比较适合入门看一下。另外作者有个建议：
理解复杂的函数有一个好的方法，那就是学习它的标志-输入和输出。
Nice way to understand complicated function is to study its signature – inputs and outputs. With pure functions, only inputs-output relation matters.
seq2seq with TensorFlow
Collection of unfinished tutorials. May be good for educational purposes.
https://github.com/ematvey/tensorflow-seq2seq-tutorials
