code: function stroke(shape, fill) {
           if (shape.shapeType === "Rectangle") {
             this.strokeRect(shape.left, shape.top, shape.width, shape.height, fill);
           } else if (shape instanceof me.Line || shape instanceof me.Polygon) {
             this.strokePolygon(shape, fill);
           } else if (shape instanceof me.Ellipse) {
             this.strokeEllipse(shape.pos.x, shape.pos.y, shape.radiusV.x, shape.radiusV.y, fill);
           }
         }
docs: stroke the given shape
  @name stroke
  @memberOf me.Renderer.prototype
  @function
  @param {me.Rect|me.Polygon|me.Line|me.Ellipse} shape a shape object to stroke