It looks like someone may have goofed with writing up the changelog, because the iPad app didn't actually get any new line spacing options. Instead it gained options for setting the left and right margins, which can be used in combination with the existing line spacing options.
That's a good thing, or at least it would be if not for the fact that this doesn't appear to use more screen space. Instead the new margin options allows you to waste more screen real estate on empty white space. Bleh.
But on the upside this app did get a cool new option for highlight across page turns. And with KPR ebooks you can now filter notes, highlights, and bookmarks by type. This will save you the effort of having to dig through a long list of annotations for the one you're looking for.
This app also includes bug fixes, and an incremental improvement to the Skynet AI that Amazon has secretly installed on all of our devices.