Add pruning support (#12)

src/user-config.dist.php

@@ -25,3 +25,16 @@ const DATABASE_NAME = 'frc.db';
  * The default, 'F j, Y \a\t g:ia', equates to "August 17, 2023 at 4:45pm"
  */
 const DATE_TIME_FORMAT = 'F j, Y \a\t g:ia';
+
+/**
+ * How should item purging be done? (Purging never applies to bookmarked items.) Options are:
+ * - Feed::PURGE_READ - Purge all read items whenever purging is run (will not purge unread items)
+ * - Feed::PURGE_BY_DAYS - Purge read and unread items older than a number of days (PURGE_NUMBER below)
+ * - Feed::PURGE_BY_COUNT - Purge read and unread items beyond the number to keep (PURGE_NUMBER below)
+ */
+const PURGE_TYPE = Feed::PURGE_BY_DAYS;
+
+/**
+ * For purge-by-days, how many days of items should be kept; for purge-by-count, how many items should be kept
+ */
+const PURGE_NUMBER = 30;