adam実装

https://github.com/pfnet/chainer/tree/master/chainer/optimizers

http://blog.csdn.net/csyanbin/article/details/53460627

https://github.com/fchollet/keras/blob/master/keras/optimizers.py

http://www.2cto.com/kf/201611/562392.html

http://blog.csdn.net/heyongluoyao8/article/details/52478715