created a Writer module that writes to an individual, provided socket

* extracted the Writer logic from app.js
created a Broadcaster module

* made the default room get stored into a constant for reusability
extracted logic into a RoomHelper module

* to check for room name availability
* display the list of rooms
* get the room count
create a SocketUsername module

* checks name availability, validity
* also assigns username
extracted logic into a Command module

* handles checking validity
* handles execution of commands
user can join different rooms
made a list of present users be printed upon joining a new room