[Feature] UTF-8 text in conversion table

[sebalis]

As many files contain UTF-8 text these days, it would seem worthwhile to not only ASCII text conversion in the conversion table but UTF-8 text as well. My idea is that it would try to decode the bytes from the current position as UTF-8 and stop as soon as the first decoding error is found (or after a maximum number of characters of course). See also #61.