[Metadata Source Plugin] Apple Books covers

[Majutsushi]

This is a bit tricky as the iTunes API is apparently somewhat inconsistent when searching for both the author and the title at the same time, as the plugin is currently doing to avoid false positives for common titles. You can see that even on the website you linked where searching for "The Fifth Season Jemisin" yields no results either (whereas something like "lord of the rings tolkien" works fine). Looks like I'll have to make the code smarter about querying more broadly and then filtering manually.