Our HTML Cleaner does not generate valid HTML5 content

Problem

The HTML Cleaner (used by the HTML Macro) generates valid XHTML1.0 code but invalid HTML5 code.

Example:

<img src="logo.png" alt="logo"></img>

(invalid)

instead of:

<img src="logo.png" alt="logo" />

(valid)

Steps to reproduce:

in a document, write:

{{html}}
<img src="logo.png" alt="logo" />
{{/html}}

You end up with

<img src="logo.png" alt="logo"></img>

Cause

The problem comes from our XML Serializer (XWikiXMLOutputter) which does not produce good HTML5 code.