new setting for deleting old entries (fix #524)

CHANGELOG

@@ -1,6 +1,7 @@
 v 2.1.0
   - dropwizard upgrade to 0.8.0
   - you have to remove the "app.contextPath" setting from your yml file, you can optionally use server.applicationContextPath instead
+  - new setting app.maxFeedCapacity for deleting old entries
   - ability to set filtering expressions for subscriptions to automatically mark new entries as read based on title, content, author or url.
   - ability to use !keyword or -keyword to exclude a keyword from a search query
   - facebook feeds now show user favicon instead of facebook favicon