修改后的版本能够处理任意尺寸的输入
定义了接口，使用方法见demo，几行的输入即可实现光流预测。
使用环境：tensorflow1.2，ubuntu16，cuda8
[1] E. Ilg, N. Mayer, T. Saikia, M. Keuper, A. Dosovitskiy, T. Brox FlowNet 2.0: Evolution of Optical Flow Estimation with Deep Networks, IEEE Conference in Computer Vision and Pattern Recognition (CVPR), 2017.
As noted in the beginning, most part are from sampepose/flownet2-tf