Scale interface and adapt to big screens

[mmuruev]

For now in 5k resolution book index looks small and can be scaled, book itself has alot of space around the text and text is also small ( which can be fixed with default font size, but its not convinient usually just Ctrl+scroll works much better), but its possible to do book a bit adaptive it has enough space it can open more then 2 pages at once( very useful for tech books), and on scale hide text. Probably also some magnify glass feature will be good.

[johnfactotum]

You can increase the maximum width/height/number of columns from the Font & Layout Settings window (Alt+,):