lots of minor-ish stuff for this batch of changes.
Biggest change is actually adding proper cli parsing and help messages! previously, the cli was extremely bare-bones and just good enough to actually work but didn’t have any decent error handling or help messages.

I’ve also ditched the option that runs the selector program (e.g. rofi, fuzzel). I didn’t know about he -nth those programs have, which let you hide data from the selector, so that functionality was kinda redundant.
(also the sizes are human-readable now, i.e. in kb/mb/gb instead of just raw bytes)