Add ability to set the feed's title

Make the list item a dict with 'url' and 'title' keys. For example:

# block style
- url: http://hnrss.org/newest?points=100
  title: Hacker News (Over 100 points)

# flow style
- {url: "http://hnrss.org/newcomments", title: "Latest Hacker News Comments"}

(Quote string if it contains a colon, otherwise it's optional.)