socket.io 官网给的例子都是需要先createServer后才能 require('socket.io')(server);
问题来了，express生成器生成的项目，createServer 是在最后/bin/www中创建的,该如何使用改写呢？

// socket.io 官网
var app = require('express').createServer();
var io = require('socket.io')(app);
...
...

/* express生成器生成的项目(下面这段是/bin/www文件)
*  想在app文件中 require('socket.io'),不会了....
*/
var app = require('../app');
var debug = require('debug')('TestServer:server');
var http = require('http');

/**
 * Get port from environment and store in Express.
 */

var port = normalizePort(process.env.PORT || '3000');
app.set('port', port);

/**
 * Create HTTP server.
 */

var server = http.createServer(app);