Typo fix.
Document the "device" keyword and its value.
Add the device parsing logic. It allows mtree's libarchive to
parse device entries like NetBSD's mtree and its multiple possible
format: native, 386bsd, 4bsd, bsdos, freebsd, hpux, isc, linux, netbsd,
osf1, sco, solaris, sunos, svr3, svr4, and ultrix.