fzy returns which characters matched the search for every item, so use
this to highlight them.
This defaults to a light blue color that is readable with both black and
white (selected) backgrounds.
The returned positions are just bytes, so we can't put ASS tags or
escape sequences around each byte because that would break displaying
multibyte UTF-8 characters. Only put them around sequences of matched
positions, and only when the sequences start and end at actual character
positions.
Guido Cella
72bb227bf1