code: function traverse(bits, src) {
    for (const code of src.keys()) {
      bits.set(code, true);
    }
  
    const buffer = bits.toBuffer();
    return Buffer.concat([createSize(buffer), buffer]);
  }
docs: Iterare over code points and
  convert it into an buffer.
  @param {bitfield} bits
  @param {Array} src
  @returns {Buffer}