Implemented a basic block caching system.

- for block {block_id}, to have a cache with 3600 seconds of expiration,
    declare in the cms.ini
     [blocks]
     {block_id}.expiration=3600

Added support for size in feed aggregation with new field "size"

examples/demo/site/config/modules/feed_aggregator/feeds.json

@@ -1,25 +1,28 @@
 {
-	"ids": ["eiffel", "forum", "stackoverflow"],
+	"ids": ["eiffel", "forum"],
 	"feeds": { 
 			"eiffel": {
 				"title": "Eiffel related posts.", 
 				"expiration": "21600",
+				"size": 10,
 				"locations": [
 						"https://bertrandmeyer.com/feed/",
-						"https://room.eiffel.com/blog/feed"
+						"https://room.eiffel.com/blog/feed",
+						"https://room.eiffel.com/article/feed",
+						"https://room.eiffel.com/library/feed"
 						]
 				, "categories": ["Eiffel"]
-				,"option_description": "disabled"
+				,"option_description": "enabled"
 				},
 			"forum": {
-				"title": "Eiffel Users Group",
-				"expiration": "43200",
-				"location": "https://groups.google.com/forum/feed/eiffel-users/msgs/atom.xml?num=15"		
-			},
-			"stackoverflow": {
-				"title": "Test",
-				"expiration": "3600",
-				"location": "http://stackoverflow.com/feeds/tag?tagnames=eiffel&sort=newest"
+				"title": "Eiffel Forum",
+				"expiration": "21600",
+				"size": 10,
+				"locations": [
+						"https://groups.google.com/forum/feed/eiffel-users/msgs/atom.xml?num=15".
+						"http://stackoverflow.com/feeds/tag?tagnames=eiffel&sort=newest"
+					]
+				,"option_description": "enabled"
 			}
 	}
 }