Convert aggregator-summary-item.tpl.php to HTML5

I removed the code in the template referring to $source_url and $source_title. Looking at the SQL query that drives the data for the items, the field feed_title is neither called from the database for the item:

db_query_range('SELECT i.title, i.timestamp, i.link FROM {aggregator_item} i WHERE i.fid = :fid ORDER BY i.timestamp DESC', 0, variable_get('aggregator_summary_items', 3), array(':fid' => $feed->fid));

nor does it exist as a field in the database for the item

+-------------+--------------+------+-----+---------+----------------+
| Field       | Type         | Null | Key | Default | Extra          |
+-------------+--------------+------+-----+---------+----------------+
| iid         | int(11)      | NO   | PRI | NULL    | auto_increment |
| fid         | int(11)      | NO   | MUL | 0       |                |
| title       | varchar(255) | NO   |     |         |                |
| link        | varchar(255) | NO   |     |         |                |
| author      | varchar(255) | NO   |     |         |                |
| description | longtext     | NO   |     | NULL    |                |
| timestamp   | int(11)      | YES  |     | NULL    |                |
| guid        | varchar(255) | YES  |     | NULL    |                |
+-------------+--------------+------+-----+---------+----------------+

This reduces the complexity of the template down to a simple link and span. I added a call to theme_datetime to render the age of the item as a <time> element.

After making these changes, I started to wonder if the template file is really even necessary. So I made a switch to a theme function for rendering source item summaries. It seems a lot cleaner than a template that gets called often to print two variables.

Great, thanks everyone!