normalizeVector = (vector, vectorMean, vectorStddev) => {
  return vector.map(x => (x - vectorMean) / vectorStddev);
}
Normalize a vector by its mean and standard deviation.

@param {Array} vector Vector to be normalized.
@param {number} vectorMean Mean to be used.
@param {number} vectorStddev Standard Deviation to be used.

@returns {Array} Normalized vector.