Don't typecast parsed document if I want

The brief history why I've commited it - I can't parse properly document like this:

```xml
<global-settings>
	<group>
		<name>Settings</name>
		<setting id="host_api_key" type="string" default-value="">
			<name>Host API Key</name>
			<description>Test</description>
		</setting>
	</group>
</global-settings>
```

```ruby
=> MultiXml.parse(xml)
=> {"global_settings"=>
  {"group"=>{"name"=>"Global CloudFlare Settings", "setting"=>""}}}
```