resize all images in the dataset and save them to `new_path`
        
        Arguments:
        targ (int): the target size
        new_path (string): the new folder to save the images
        resume (bool): if true (default), allow resuming a partial resize operation by checking for the existence
        of individual images rather than the existence of the directory
        fn (function): custom resizing function Img -> Img

def resize_imgs(self, targ, new_path, resume=True, fn=None):
        """
        resize all images in the dataset and save them to `new_path`
        
        Arguments:
        targ (int): the target size
        new_path (string): the new folder to save the images
        resume (bool): if true (default), allow resuming a partial resize operation by checking for the existence
        of individual images rather than the existence of the directory
        fn (function): custom resizing function Img -> Img
        """
        dest = resize_imgs(self.fnames, targ, self.path, new_path, resume, fn)
        return self.__class__(self.fnames, self.y, self.transform, dest)