[FEATURE] Exporting highlights, annotations and bookmarks

[hollisticated-horse]

Is your feature request related to a problem? Please describe.

When planning for highlights, annotations and bookmarking (see #115 ) for epubs (maybe pdf and cbz/cb ?), a very important feature is being able to export this content for use elsewhere.

Describe the solution you'd like
At least two elements come to mind:

1. export per book/media
2. Global export, dated.

Maybe out of this scope, a way to see and edit those annotations, per media and/or globally.

Describe alternatives you've considered

Will be modified if anything comes to mind.

Additional context

• Koreader Guide on Bookmarks
• https://manual.calibre-ebook.com/viewer.html#highlighting-text