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"

src/kernel/content/cms_cache_block.e

@@ -0,0 +1,99 @@
+note
+	description: "[
+			CMS_BLOCK implemented with a `cache'
+			as caching solution.
+		]"
+	date: "$Date: 2014-11-18 10:13:13 +0100 (mar., 18 nov. 2014) $"
+	revision: "$Revision: 96110 $"
+
+class
+	CMS_CACHE_BLOCK
+
+inherit
+	CMS_BLOCK
+
+create
+	make
+
+feature {NONE} -- Initialization
+
+	make (a_name: like name; a_cache: like cache)
+		require
+			a_name_not_blank: not a_name.is_whitespace
+		do
+			is_enabled := True
+			name := a_name
+			cache := a_cache
+			set_is_raw (True)
+		end
+
+feature -- Access
+
+	name: READABLE_STRING_8
+			-- <Precursor>
+
+	title: detachable READABLE_STRING_32
+			-- <Precursor>
+
+	cache: CMS_CACHE [READABLE_STRING_8]
+			-- Cache content.
+
+feature -- Status report
+
+	is_empty: BOOLEAN
+			-- Is current block empty?
+		do
+			Result := is_raw and not cache.exists
+		end
+
+	is_raw: BOOLEAN assign set_is_raw
+			-- Is raw?
+			-- If True, do not get wrapped it with block specific div	
+
+feature -- Element change
+
+	set_is_raw (b: BOOLEAN)
+		do
+			is_raw := b
+		end
+
+	set_name (n: like name)
+			-- Set `name' to `n'.
+		require
+			not n.is_whitespace
+		do
+			name := n
+		end
+
+	set_title (a_title: like title)
+			-- Set `title' to `a_title'.
+		do
+			title := a_title
+		end
+
+feature -- Conversion
+
+	to_html (a_theme: CMS_THEME): STRING_8
+		do
+			debug
+				print ("REUSE CACHE for [" + name + "]!!!%N")
+			end
+				-- Why in this particular case theme is not used to generate the content?
+			if attached cache.item as l_content then
+				Result := l_content
+			else
+				Result := ""
+				check exists: False end
+			end
+		end
+note
+	copyright: "2011-2015, Jocelyn Fiat, Javier Velilla, Eiffel Software and others"
+	license: "Eiffel Forum License v2 (see http://www.eiffel.com/licensing/forum.txt)"
+	source: "[
+			Eiffel Software
+			5949 Hollister Ave., Goleta, CA 93117 USA
+			Telephone 805-685-1006, Fax 805-685-6869
+			Website http://www.eiffel.com
+			Customer support http://support.eiffel.com
+		]"
+end