Training example at large or median scale

[lgarithm]

Now we have demonstrated the possibility of implementing well known models with crystalnet, by giving two examples: vgg16 and yolov2.

But we still don't have an example of training the model from scratch.

We need to choose a model that isn't too small, but also not too large, and build a training example for it.

[lgarithm]

@luomai @zsdonghao any suggestions?

[luomai]

resnet-50 is a good choice.