Express migrating from 3.x to 4.x

[JerryChin]

Due to the overhaul of express, most of code in app.js has broken, as dalareo experienced (see #17). I've made some changes according to Migrating from 3.x to 4.x, with the intention of least being able to start the server, so there're possibly some other issues or warning, but beyond my concern, hope someone will fix it for the sake of performance and security.