BridgeAbstract will return 3600 seconds by default, so the function
can be removed from any bridge implementing getCacheDuration
returning the same value.
Documentation updated accordingly.
On searches for popular keywords, a feed reader not reading the feed often
enough can miss items (ie more than 5 items were added since last fetch)
so this change increases the limit from 5 items to 10 items, and retrieves
pages faster to compensate (500ms seems enough for not spamming t411).
