revise auth.js and route.js to make it work correctly
changed a bit about the auth.js.
we need consider it carefully.
e.g.:
auth is to check whether a user is logged in or  persisten login, it is is. we will assign req.session.userId a value. otherwise this one will be undefined or null.
then according to this value to decide the jump strategy in each function.
 if app.get('/home'),  no matter what, jump to home.
    app.get('/works'), if no login, jump to home, otherwise jump to works page.
    app.get('/topic/create'), if not login, jump to login page. otherwise go to create page.