[fix] fallback to next middleware if there is no rule.

[doc] add readme

index.js

@@ -47,8 +47,9 @@ module.exports = function (urls) {
         // If routing to a server on another domain, the hostname in the request must be changed.
         req.headers.host = m.host;
         // Once any changes are taken care of, this line makes the magic happen.
-        proxy.proxyRequest(req, res, m.dest);
+        return proxy.proxyRequest(req, res, m.dest);
       }
     }
+    next() //did not have a rule for this request. fall back to next middleware.
   }
 }

readme.markdown

+#proxy by url
+
+this is a simple example of a node-http-middleware that will proxy based on the incoming url.
+say you want to proxy every request thing under /database to localhost:5984 (couchbd)
+(and remove the /database prefix)
+
+this is how:
+
+    require('http-proxy').createServer(
+      require('proxy-by-url')({
+        '/database': { port: 5984, host: 'localhost' },
+      })
+    ).listen(8000)