use new response module for assets

unfortunately we can't use stream pipes because we need to generate
a hash of the content for the Etag.

I think proper caching (i.e. Etag) is very important

lib/server.js

@@ -18,20 +18,20 @@ var routes = {
   capes: require("./routes/capes")
 };
 
-function asset_request(req, res) {
+// serves assets from lib/public
+function asset_request(req, callback) {
   var filename = path.join(__dirname, "public", req.url.path_list.join("/"));
   fs.exists(filename, function(exists) {
     if (exists) {
-      res.writeHead(200, {
-        "Content-type": mime.lookup(filename),
-        "Cache-Control": "max-age=7200, public", // cache for 2 hours
+      fs.readFile(filename, function(err, data) {
+        callback({
+          body: data,
+          type: mime.lookup(filename),
+          err: err
+        });
       });
-      fs.createReadStream(filename).pipe(res);
     } else {
-      res.writeHead(404, {
-        "Content-type": "text/plain"
-      });
-      res.end("Not Found");
+      callback({});
     }
   });
 }
@@ -95,7 +95,9 @@ function requestHandler(req, res) {
         });
         break;
         default:
-        asset_request(req, res);
+        asset_request(req, function(result) {
+          response(req, res, result);
+        });
       }
     } catch(e) {
       var error = JSON.stringify(req.headers) + "\n" + e.stack;