add depth family

[plastikfan]

Add --depth and --skim(K) flags. --skim is the opposite of --recurse and is primarily designed for the navigator in extendio, but since the raison d'etre of the navigator is to recurse, that should be default, so we need the oppose of that to set the navigator to just navigate the directory specified, without recursing.

actually, the --cpu and --now flags are niche so not valid to be using up short codes (-C and -N); the short codes will be removed.