add lib/redis and lib/mongodb lib in order to replace  lib/db
add lib/session to configure session management stuff for express app
remove lib/db reference and replace with lib/redis
change its format
apply to use lib/session for session management instead of old style
exports Deal directly instead of exports.Deal
remove lib/db.js since we have lib/redis.js and lib/mongodb.js
exports mongoose directly and use logger instead of console
change tu import mongoose directly
add a nodeunit test for Deal