change font-color for differing digits in comparator

[gdementen]

Often the differences are after a few digits, but I often find myself squinting at my screen to determine the first different digit.
If all the different digits were red, it would make the process much faster.

Unsure how hard this would be. I suppose Qt supports this but...

[gdementen]

Surprisingly, Qt does NOT support this natively (at least as of Qt5). With some ugly hacks, it is possible to render html in cells though. Unsure the limited html in Qt will support span colors, but that would at least provide <b>changed digits</b> which would work just as well I think.

The ugly hack below seems slow, but might be fast enough anyway, especially with the buffer branch.

See:
https://stackoverflow.com/a/66091713/288162
and:
https://stackoverflow.com/questions/35397943/how-to-make-a-fast-qtableview-with-html-formatted-and-clickable-cells