get0(N) unifies N with the ASCII code of the next
character from the current input stream. Cf. ttyget0/1.
get(N) unifies N with the ASCII code of the next
non-layout character from the current input stream. Layout characters
are all outside the inclusive range 33..126; this includes space, tab,
linefeed, delete, and all control characters. Cf. ttyget/1.