Fixed offset marker

[raspi]

Add --marker parameter which marks every N bytes with visual marker. Highlight with some color and/or add bold/underline effect.

The use case is file formats that use fixed block size(s). Marker helps to see where next block starts/ends.

Example:

heksa --marker 1KiB

It could also be some sort of loop:

heksa --marker 1KiB,2KiB,5B

This would set first marker at 1 KiB, then the next (last + 2KiB) and the next (last + 5 B) and then again (last + 1 KiB) and so on..