Store just the indices of the matching items in matches. The text is
looked up in selectable_items, and the positions to highlight are
computed in get_matches_to_print() only for the rendered matches, using
the query that produced the current matches. This reduces useless work
of computing highlight positions when only handful of items can be
displayed at the time on screen in practice.
Sort matches without lua comparator, this significantly speeds up
sorting of big lists, where C->Lua round-trip was problematic.
Overall it's 10x-20x times faster in my testcase.
Kacper Michajłow
893ffae982