[WIP] Implement conditional highlighting of permissions, user and group

[xPMo]

Two methods, currently set by K_PERM_COLOR

• absolute: u ⇒ green, g ⇒ yellow, o ⇒ red (same as grc)
• relative: u,g ⇒ fade if user doesn't have UID/GID

This PR also:

• Only fades the owner and group if the UID and GID matches
• colors all link permissions with K_COLOR_LN, since they don't have any bearing on the actual permissions used.

Unfortunate consequences of the methods I used:

• Runs zstat a second time on every file, to get numeric values for uid and gid. (OTOH, this does bring up possibilities for using numeric values elsewhere for speed. date/time methods especially)
• Uses a few temp variables to do add color in the ${string//match/replacement}

If there is interest, I would be happy to change things, clean this up, split this it up atomically, get it merge-ready.

[xPMo]

Alternate relative method: Don't fade all the -s, just each (rwx) column group.