Consider storing percentage completed in the database

[Earnestly]

It would be quite nice to have a reliable means to determine completion of various documents directly from the databases (or elsewhere, such as a sioyek cli query) so that I can include this information in my various simple menus.

For pdf documents this is fairly simple but with epubs and such the font size can be changed which increases the page count; so the ratio between current page and total pages can float.

A value between 0 and 1 expressing this ratio would be quite nice to have, either via database (sql) or command-line query flag.