ability to change publisher

[anandkumarpatel]

create a new publisher which is just an event emitter. this way people can use this module inside their own apps without having to publish to redis. this helps for applications running on same box as docker.

the goal is to be able to do this

process.env.EMITER_TYPE=emitter
var event = require('docker-listener')
event.on('container:die, handleDie)'

we should switch between redis publisher and event emitter via ENV var.