Etching in the door service and characteristic.
Updating the README for the door peripheral.
Removing unused callbacks
Updating the text that is printed when the peripheral is started to communicate the primary service UUID.
Updating Authentication to rely on a JSON file which uses tokens as the keys to verify if a given token is allowed to open the door.

Uses environment variable:
    ALLOWED_FILE=/path/to/allowed.json
Updating README.
Updating Door#open to look for a DOOR_OPEN_COMMAND
environment variable which it will use to open 
the door.
Merge branch 'door-service' into dev