Made code leaner by outsourcing routes logic to controllers and updated the entire project to use ES6+ syntax

[Sayan3sarkar]

Hey,

The following is the list of changes I made and these changes are causing the app to behave exactly the same as running the app on the master branch would.

1. Updated the entire project to use ES6+ syntax like let/const instead of var and Arrow functions in place of 'function'.
2. Outsourced all the logic of the files inside routes/api directory to have a controller based apporach by putting the internal logic in controllers folder. This gives the app a MVC like architecture and makes the code leaner.

The latest commit has all these changes covered.

Kindly merge this request.

Regards,
Sayan Sarkar

[ctrngk]

Unfortunately it is not working

TypeError: this.generateJWT is not a function
at model.UserSchema.methods.toAuthJSON (node-express-realworld-example-app/models/User.js:46:17)