Show the `xs` (inputs) and `ys`(targets)  on a figure of `figsize`.

def show_xys(self, xs, ys, imgsize:int=4, figsize:Optional[Tuple[int,int]]=None, **kwargs):
        "Show the `xs` (inputs) and `ys`(targets)  on a figure of `figsize`."
        axs = subplots(len(xs), 2, imgsize=imgsize, figsize=figsize)
        for i, (x,y) in enumerate(zip(xs,ys)):
            x.show(ax=axs[i,0], **kwargs)
            y.show(ax=axs[i,1], **kwargs)
        plt.tight_layout()