Include summaries in the recent articles list if RECENT_ARTICLE_SUMMARY is set.

As mentioned in #120, I would like to have summaries on my "recent articles" list on the main page. I have resurrected the relevant part of the template from the revision mentioned there and wrapped it in a check for the presence of the (new) `RECENT_ARTICLE_SUMMARY` config variable.

As I suspected, the styling isn't quite right and will probably have to be tweaked by someone with more skill than I in that area. (If you decide that this isn't something you want in your theme, I'm happy to maintain my own fork for my personal webite.)