function scaling(v, dst) {
  dst = dst || new MatType(16);
  dst[0] = v[0];
  dst[1] = 0;
  dst[2] = 0;
  dst[3] = 0;
  dst[4] = 0;
  dst[5] = v[1];
  dst[6] = 0;
  dst[7] = 0;
  dst[8] = 0;
  dst[9] = 0;
  dst[10] = v[2];
  dst[11] = 0;
  dst[12] = 0;
  dst[13] = 0;
  dst[14] = 0;
  dst[15] = 1;
  return dst;
}
Creates a 4-by-4 matrix which scales in each dimension by an amount given by
the corresponding entry in the given vector; assumes the vector has three
entries.
@param {module:twgl/v3.Vec3} v A vector of
    three entries specifying the factor by which to scale in each dimension.
@param {module:twgl/m4.Mat4} [dst] matrix to hold result. If not passed a new one is created.
@return {module:twgl/m4.Mat4} The scaling matrix.
@memberOf module:twgl/m4