Proposed FORMAT features

[Guy Steele <GLS at SU-AI>]

CC:   GLS at SU-AI   

(a) Let some modifier, e.g. :, make G be a relative GOTO rather than
    an absolute one.  This is useful for processing some argument twice.
    (Maybe this already exists if * can take a negative arg?!)
(b) Let , _, and  (right, left, and double arrow) also be modifiers.
    If the field width is fixed, then these modifiers cause the stuff
    to be right, left, or center justified within the field.  I have
    often wanted a right-justified ~S or a left-justified ~D.