Add supports for ignoring regions

CLI parameter could be the same as [yahoo/blink-diff](https://github.com/yahoo/blink-diff):

```
--block-out x,y,w,h Block-out area. Can be repeated multiple times.
```

Usage for example:

```
dify tiger.jpg tiger-2.jpg --block-out 0,0,10,10 --block-out 20,20,10,10
```
