function lerp(out, a, b, t) {
  var ax = a[0];
  var ay = a[1];
  var az = a[2];
  var aw = a[3];
  out[0] = ax + t * (b[0] - ax);
  out[1] = ay + t * (b[1] - ay);
  out[2] = az + t * (b[2] - az);
  out[3] = aw + t * (b[3] - aw);
  return out;
}
Performs a linear interpolation between two vec4's

@param {vec4} out the receiving vector
@param {vec4} a the first operand
@param {vec4} b the second operand
@param {Number} t interpolation amount between the two inputs
@returns {vec4} out