Provide multiple author names in RSS feed items

[johnbillion]

When a post is attributed to multiple authors they should all be displayed in the RSS feed item for that post. WordPress uses the Dublin Core namespace for author information in the <dc:creator> element.

The RSS spec is famously vague. The RSS Best Practices Profile says An item MAY contain more than one dc:creator element to credit multiple authors but in practice it seems that RSS clients only display the first. For example SimplePie fully supports multiple <dc:creator> elements but the RSS widget in WordPress core will only display the first.

This means that multiple authors should all be listed in the same <dc:creator> element.

The data for this element comes from the_author() so this might be implemented at that level. Needs investigation as the_author() is used in many places.