title: how to serialize a YamlDocument to yaml string
body: <p>I use YamlDotnet and I have a YamlDocument. Now I want to convert it to his yaml text representation in memory but I don't see how to achieve that.</p>
  
  <pre><code>var yaml = new YamlDocument(new YamlMappingNode());
  yaml.Add("one", "other")
  var text = yaml.ToYamlText()
  </code></pre>
  
  <p>and I should get in text something like :</p>
  
  <pre><code>one: "other"
  </code></pre>
  
  <p>I tried zith Serializer class but with no success</p>