docs: function open(path, writable) {
    assert.string(path, 'path');
    assert.optionalBool(writable, 'writable');
    writable = writable === true;
    let flags = 'r';
    if (writable) {
      flags += '+';
    }
    return fsAccess(path)
      .then(() => fsOpen(path, flags))
      .then(fd => fsStat(fd)
        .then(st => new RandomAccessFile(path, fd, st.size, writable)));
  }