code: function enlarge(object, x, y, z) {
    var a;
    if (Array.isArray(x)) {
      a = x;
    } else {
      a = [x, y, z];
    }
  
    var size = util.size(object);
    var centroid = util.centroid(object, size);
  
    var idx = 0;
  
    var t = util.map(size, function(i) {
      return util.scale(i, a[idx++]);
    });
  
    var new_object = object.scale(t);
    var new_centroid = util.centroid(new_object);
  
    /// Calculate the difference between the original centroid and the new
    var delta = new_centroid.minus(centroid).times(-1);
  
    return new_object.translate(delta);
  }
docs: Enlarge an object by scale units, while keeping the same
  centroid.  For example util.enlarge(o, 1, 1, 1) enlarges
  object o by 1mm in each access, while the centroid stays the same.
  @param  {CSG} object [description]
  @param  {number} x      [description]
  @param  {number} y      [description]
  @param  {number} z      [description]
  @return {CSG}        [description]