added auth API, /auth/login, /auth/logout.  But both of them are test
implementation.

To use auth API, you need several steps.
1. insert user data.
1.1. mongo (run console)
1.2. use atmosphere
1.3. db.users.insert({"username":"name of user", "password":"password
for user"})

Usage:
1. call /auth/login with post data {"user_id":"...", "password":"..."}
2. response {"session_id":"..."}
3. call /auth/logout with post data {"session_id":"..."}

Known issues:
1. session_id must be stored into header of request/response.
2. password must be encripted(hash + salt).