XML output support

[annavanbiemen]

The Output class should be able to produce XML responses using either an

• XML string
• SimpleXMLElement instance
• DOMDocument instance

[annavanbiemen]

On second thought... automatically detecting the type of XML argument passed adds complexity while the caller can just simply use a single method call to the appropriate API to convert any SimpleXMLElement or DOMDocument instance into a string.

A string-only API should suffice:

public function xml(string $document): Response

[baukevdw]

Or register an xml handler like this:

$output->register(SimpleXMLElement::class, function (SimpleXMLElement $xml) use ($output): Response {
    return $output->text($xml->asXML())->withContentType('text/xml');
});

An XML handler that set's the header would be an useful addition though.

[annavanbiemen]

Added the xml handler with just a text/xml Content-Type.