criteria: Misclassification

There are two ways to use the API:

To use the criteria:
```python
raw_advs, clipped_advs, success = attack(fmodel, data, criterion=Misclassification(label), epsilons=args.eps)
```

and without using the criteria:
```python
raw_advs, clipped_advs, success = attack(fmodel, data, label, epsilons=args.eps)
```

What is the difference?
Unfortunately, haven't found examples anywhere.