Purpose: Add the map coordinates to the Mr Mail Tracker database for the all the cities and ZIP codes in a particular mailing list.
        Example URL:
        https://MrMailTracker.com/api/process_geocodes?login_id=49&user_id=20&key=GsF6CkPmErRh&mailing_id=55382
    
Sample response:
{
    "response": "success"
}
        
        There's no data returned from the API.  After the coordinates have been
        retrieved, they are stored in the Mr Mail Tracker database.  The
        coordinates can then be retrieved by making a call to the API at the path
        /api/track_mailing_city
        or
        /api/track_mailing_zip.
    
    Note: once the coordinates for a particular city or ZIP code have been retrieved and added to the database, they will be available to all future mailings without calling this function in the API.