def deflate!(by_w, by_h = nil)
      if by_w.respond_to? :width
        inflate!(-by_w.width, -by_w.height)
      else
        inflate!(-by_w, -by_h)
      end
    end
def deflate!(by_w, by_h = nil)
      if by_w.respond_to? :width
        inflate!(-by_w.width, -by_w.height)
      else
        inflate!(-by_w, -by_h)
      end
    end
DEcrease the dimensions of the current Size in the width direction
 by +by_w+ and in the height direction by +by_h+.

 by_w and by_h can be a Fixnum, or another Size.