[FIX] respect nconf hierarchy behavior

read config to it's own namespace to avoid overriding all previously configured settings. With this behavior any of existing nconf parameters will still exist and will only be overridden if there's a clash
[FIX] lint errors
[DOC] update readme with option config example

and tidy up a bit
[CHORE] move default config file to simple-sqs-queue.config.json

to avoid accidental clashes