function merge(from, to) {
  assert.ok(from);
  assert.equal(typeof(from), 'object');
  assert.ok(to);
  assert.equal(typeof(to), 'object');

  var keys = Object.getOwnPropertyNames(from);
  keys.forEach(function(key) {
    if (to[key])
      return;

    var value = Object.getOwnPropertyDescriptor(from, key);
    Object.defineProperty(to, key, value);
  });

  return to;
}
Parses the next sequence in this BER buffer.

To get the length of the sequence, call `Reader.length`.

@return {Number} the sequence's tag.