几篇讲优化器的好文，mark一下
英文Optimizer overview
http://ruder.io/optimizing-gradient-descent/index.html#adam
Optimization for Deep Learning
http://ruder.io/deep-learning-optimization-2017/index.html
中文overview
https://www.jianshu.com/p/0acd30a23e4e
Adam讲解：
https://www.jianshu.com/p/aebcaf8af76e
多图汇总
https://blog.csdn.net/qsczse943062710/article/details/76763739