docs: function randomBits (n) {
    if (typeof n !== 'number') throw new Error('bitString#randomBits: Need number');
    var buf = _randomBytes(Math.ceil(n/8)),
        bits = '';
    for (var i = 0; i < n; i++) {
      bits += (buf[Math.floor(i / 8)] & (0x01 << (i % 8))) ? '1' : '0';
    }
    return bits;
  }