code: function stretch(object, axis, distance, offset) {
    var normal = {
      x: [1, 0, 0],
      y: [0, 1, 0],
      z: [0, 0, 1]
    };
    var bounds = object.getBounds();
    var size = util.size(object);
    var cutDelta = util.getDelta(size, bounds, axis, offset, true);
    // console.log('stretch.cutDelta', cutDelta, normal[axis]);
    return object.stretchAtPlane(normal[axis], cutDelta, distance);
  }
docs: Wraps the `stretchAtPlane` call using the same
  logic as `bisect`.
  @param  {CSG} object   Object to stretch
  @param  {String} axis     Axis to streatch along
  @param  {Number} distance Distance to stretch
  @param  {Number} offset   Offset along the axis to cut the object
  @return {CSG}          The stretched object.