function multiplyScalar(out, a, b) {
  out[0] = a[0] * b;
  out[1] = a[1] * b;
  out[2] = a[2] * b;
  out[3] = a[3] * b;
  out[4] = a[4] * b;
  out[5] = a[5] * b;
  return out;
}
Multiply each element of the matrix by a scalar.

@param {mat2d} out the receiving matrix
@param {mat2d} a the matrix to scale
@param {Number} b amount to scale the matrix's elements by
@returns {mat2d} out