The imported library is called 'app'

Hi, I want to use this as a library for one of my projects...but to import it I have to use the code:
```
import app
```

I think it's a bit inappropriate to label this code as `app` as that's very generic, and many other packages also have submodules called `app`. Could we please rename it to something else, perhaps `rich_diff`?

Thank you,
Ryan