Prevent assets cache

Use assets url with its md5 hash

Author: june29

index.haml

@@ -1,3 +1,4 @@
+- require "digest/md5"
 - title = "Kosen Advent Calendar"
 
 !!! 5
@@ -15,10 +16,10 @@
     %meta(property="og:image"       content="http://kosenconf.github.com/advent/assets/kosen50.png"  )
     %script( type="text/javascript" src="assets/jquery-1.8.3.min.js" )
     %script( type="text/javascript" src="assets/knockout-2.2.0.js" )
-    %script( type="text/javascript" src="assets/entries.js" )
-    %script( type="text/javascript" src="assets/advent.js" )
+    %script( type="text/javascript" src="assets/entries.js?#{Digest::MD5.hexdigest(open('assets/entries.js').read)}" )
+    %script( type="text/javascript" src="assets/advent.js?#{Digest::MD5.hexdigest(open('assets/advent.js').read)}" )
     %link( rel="stylesheet" type="text/css" href="assets/bootstrap/css/bootstrap.min.css" )
-    %link( rel="stylesheet" type="text/css" href="assets/advent.css" )
+    %link( rel="stylesheet" type="text/css" href="assets/advent.css?#{Digest::MD5.hexdigest(open('assets/advent.css').read)}" )
 
     %script( type="text/html" id="entry-template" )
       .entry

index.html

@@ -14,10 +14,10 @@
     <meta content='http://kosenconf.github.com/advent/assets/kosen50.png' property='og:image' />
     <script src='assets/jquery-1.8.3.min.js' type='text/javascript'></script>
     <script src='assets/knockout-2.2.0.js' type='text/javascript'></script>
-    <script src='assets/entries.js' type='text/javascript'></script>
-    <script src='assets/advent.js' type='text/javascript'></script>
+    <script src='assets/entries.js?ca76f193b854e114fdb748e1b428ae83' type='text/javascript'></script>
+    <script src='assets/advent.js?3853a439246211f8d103c206bd65d22a' type='text/javascript'></script>
     <link href='assets/bootstrap/css/bootstrap.min.css' rel='stylesheet' type='text/css' />
-    <link href='assets/advent.css' rel='stylesheet' type='text/css' />
+    <link href='assets/advent.css?b73f2d5fe04eb651532ed838e89dcd3a' rel='stylesheet' type='text/css' />
     <script id='entry-template' type='text/html'>
       <div class='entry'>
         <h4>