Just by tweaking the SQL queries, and adding an index
on page_stat_data(start_time).
Also, in the hourly histogram, show at least a 1px bar
when there was any reading this hour.
Also adds options to remove statistics for books
with low reading duration (to clean up stats for
books just quickly browsed and not yet read).
Also adds TextWidget:getFontSizeToFitHeight()
even if we ended up not using it.
