function mulScalar(v, k, dst) {
  dst = dst || new VecType(3);
  dst[0] = v[0] * k;
  dst[1] = v[1] * k;
  dst[2] = v[2] * k;
  return dst;
}
Multiplies a vector by a scalar.
@param {module:twgl/v3.Vec3} v The vector.
@param {number} k The scalar.
@param {module:twgl/v3.Vec3} [dst] vector to hold result. If not new one is created.
@return {module:twgl/v3.Vec3} The scaled vector.
@memberOf module:twgl/v3