hexncpy.9: Some little cleanup.
kether_ntoa.9: Mention %D.

Also, perform some minor cleanup.
games/atc: Fix a logic bug.

The original logic should have really been:

if ((l < 'a' && l > 'z') || (l < 'A' && l > 'Z'))

But using islower()/isupper() is simpler and more readable.

Taken-from: NetBSD