Add Element::find()

[ThomasWeinert]

Evaluates the expression expecting a node list, but returns a FluentDOM\Query instance.

Usage:

$dom = new FluentDOM\Document();
$dom->loadXml($xml);

foreach ($dom->find('//atom:entry') as $entry) {
  echo $entry->find('atom:title')->text();
}

This allows an alternative access to the fluent api.