'add_random_crop.
Randomly crop a picture according to \'crop_shape\'. An optional padding
can be specified, for padding picture with 0s (To conserve original
image shape).
Examples:
```python
# Example: pictures of 32x32
imgaug = tflearn.ImageAugmentation()
# Random crop of 24x24 into a 32x32 picture => output 24x24
imgaug.add_random_crop((24, 24))
# Random crop of 32x32 with image padding of 6 (to conserve original image shape) => output 32x32
imgaug.add_random_crop((32, 32), 6)
Arguments:
crop_shape: `tuple` of `int`. The crop shape (height, width).
padding: `int`. If not None, the image is padded with \'padding\' 0s.
Returns:
Nothing.'

def add_random_crop(self, crop_shape, padding=None):

    self.methods.append(self._random_crop)
    self.args.append([crop_shape, padding])
