limit feed size to 20 items;

main.py

@@ -146,6 +146,7 @@ def by_feed_name(slug):
     gen.link(href=feed.atom_id)
     gen.description(feed.description)
 
+    count = 0
     for item in feed.items.order_by(Item.date):
         fe = gen.add_entry()
         fe.id(item.atom_id)
@@ -155,6 +156,10 @@ def by_feed_name(slug):
         date = item.date.replace(tzinfo=timezone.utc)
         fe.published(date)
 
+        count += 1
+        if count == 20:
+            break
+
     return gen.rss_str(pretty=True).decode('utf8')