EPUB Page References Impractical

[isosphere]

For EPUB annotations, our page references look like this:

/body/DocFragment[10]/body/p[20]/text()[1].115

This is not fit for purpose, if a user is going to try and find the source of their annotation.

There's a setting in KOReader that allows embedding the current page number (affected by layout) to the annotation, which might help. If that's the best way forward, we should adjust the README.md to suggest it, and then we can maybe add extra support for handling that.

This issue was spurred by this post on the Mobile Read forums: https://www.mobileread.com/forums/showpost.php?p=4397442&postcount=2

[isosphere]

This PR might help: koreader/koreader#11464