Impossible to use Macros with content when using the MediaWiki syntax

The reason is that in org.xwiki.rendering.wikimodel.mediawiki.MediaWikiMacroParser there's:

public WikiMacro parse(String str)
{
  String name = null;
  String definition = str;
...
  return new WikiMacro(name, params, definition);
}

However the 3rd param of WikiMacro is supposed to be the content. The problem is that here it's being passed the full string. For example if you have:

{{macro|param=1}}

then content will be

{{macro|param=1}}

I think we could either decide that there's a special parameter for content such as "content" or if the parameter is unnamed and the last one then use that as the content.