code: public static String makeMarginTransform(double owidth, double oheight, double iwidth, double iheight, double margin) {
      return makeMarginTransform(owidth, oheight, iwidth, iheight, margin, margin, margin, margin);
    }
docs: Make a transform string to add margins
  
  @param owidth Width of outer (embedding) canvas
  @param oheight Height of outer (embedding) canvas
  @param iwidth Width of inner (embedded) canvas
  @param iheight Height of inner (embedded) canvas
  @param margin Margin (in inner canvas' units)
  @return Transform string