Add zone middleware

lib/middleware/zone.js

@@ -0,0 +1,14 @@
+require('zone').enable();
+
+module.exports = context;
+
+function context(options) {
+  return function(req, res, next) {
+    zone.create(function RequestZone() {
+      zone.data.url = req.url;
+      next();
+    }).catch(function(err) {
+      console.error(err.zoneStack + '\n');
+    });
+  };
+}