Results archiving

Added results archiving.
Result files are archived if the number of .json files exceeds n (specified in config). For each n files, a new archive is created (encoding specified in config).
Archive files are deleted after being sent to the server.
If you give tar.add() just the path, it will add the directory hierarchy to the archive (e.g. "/home/person/.centinel/results/xyz.json" will carry over the entire directory structure to the archive). Adding arcname will override this.