LibXML XmlMini parser does not handle cdata

When using LibXML-ruby as the XmlMini backend, cdata elements do not get parsed correctly into the params hash.

e.g.

<blog>
  <posts type="array">
    <post>
      <title>A blog post</title>
      <source><![CDATA[<h1>A blog post about xml cdata</h1>]]></source>
    </post>
  </posts>
</blog>

Should be mapped into the params hash as:

 {"blog" => {"posts" => [{"post" => {"title" => "A blog post", "source" => "<h1>A blog post about xml cdata</h1>"}}]}}

However, it maps in like this instead:

 {"blog" => {"posts" => [{"post" => {"title" => "A blog post", "source" => {""=>nil}}}]}}

The fix was fairly simple and just involved changing the if statement in 'to_hash' to make sure it checked for text and cdata. In addition, I copied over the nokogiri test suite just to make sure there was some basic test coverage for LibXML ruby and to verify that this fix does indeed work.