because ASCII dump is usually useless, unless there is an ASCII string, in which case the HEX part is useless

Hex:

• ASCII chars are replaced as .
• 00 is replaced by " "
• FF is replaced by "##"
• other chars are returned as hex

Output:

• a hex ruler is shown at the top of the 'display'
• offsets don't contain superfluous 0
• offsets are removed identical starting characters if following the previous
• lines full of 00 are skipped
• offsets after a skip are fully written
• Last_Offset+1 is marked with "]" (because EOF could be absent)