Since the bookmarks table is sorted based on the bookmarks'
position in the book, it is possible to sort clippings in
the exporter plugin based on that.
I've implemented a better JSON export format that removes redundant lists and objects and introduces the `entries` key containing all the entries.
It also add `drawer` values from highlight so that user can use this piece of metadata to generate desirable output.
This extends exporter.koplugin with support for [Readwise.io](https://readwise.io), a highlight/notes aggregation service.
[Readwise API documentation](https://readwise.io/api_deets)
This additionally improves the highlight exporter's ability to get the correct title and author of a document, by checking actual metadata instead of inferring from filename. It also includes a modification to the plugin's highlight parsing logic to separate the highlight contents in `.text` from the notes in `.note`. This change actually fixes an existing bug in the HTML export template note.tpl, which has been missing notes because of the lack of the `.note` field.
