This makes the [gallery] output more configurable and useful. Changes include:
* 'Description' (excerpt) is now 'Caption'
* Captions are displayed below thumbs in the main gallery display
* Thumb gallery markup is improved (dl/dd/dt for icon and caption display, tags are configurable by attributes like [gallery itemtag="div"] if necessary)
* Parent id is selectable, e.g. [gallery id=123]
* Icon size is selectable, [gallery size="medium"]
* Column count is selectable, [gallery columns=4]
* Order is selectable, [gallery orderby="post_title"]
I think some of these attributes should have a UI, where you click on the Insert Gallery Into Post button, but that's not included in this patch.
The dl/dd/dt method of marking up images with captions is discussed and recommended here:
http://www.dzr-web.com/people/darren/blog/2005/02/09/image-captions-in-xhtml/
http://www.tjkdesign.com/articles/how_to_style_thumbnail_and_caption.asp