Add predictor exporter save/load example to the MNIST tutorial
Add predictor exporter save/load example to the MNIST tutorial

Summary: Provide sample code for saving/restoring the model to/from a file

Reviewed By: salexspb

Differential Revision: D5350617

fbshipit-source-id: b5cb47e06023201b21807dafe662101b9e654350

davinwang/caffe2,Yangqing/caffe2,pietern/caffe2,pietern/caffe2,davinwang/caffe2,davinwang/caffe2,davinwang/caffe2,Yangqing/caffe2,xzturn/caffe2,bwasti/caffe2,sf-wind/caffe2,Yangqing/caffe2,sf-wind/caffe2,xzturn/caffe2,bwasti/caffe2,sf-wind/caffe2,bwasti/caffe2,davinwang/caffe2,Yangqing/caffe2,bwasti/caffe2,pietern/caffe2,xzturn/caffe2,bwasti/caffe2,xzturn/caffe2,Yangqing/caffe2,caffe2/caffe2,xzturn/caffe2,pietern/caffe2,sf-wind/caffe2,sf-wind/caffe2,pietern/caffe2