def inflate!(by_w, by_h = nil)
      return inflate_by_size(by_w) if by_w.respond_to? :width

      validate(by_w, by_h)

      @width  += by_w
      @height += by_h

      self
    end
def inflate!(by_w, by_h = nil)
      return inflate_by_size(by_w) if by_w.respond_to? :width

      validate(by_w, by_h)

      @width  += by_w
      @height += by_h

      self
    end
INcrease 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.