Replace print to logger.debug()
save_db() only take dict() type data.
* Fix log bug
* Add some test cases.
typo
Refactor: use start_backup() to replace periodic_backup_db()
Fix: Daemon Thread restart problem. (need to reinitialize)
* Add self.db_status to indicate what type of db it use when class initialize.
* Refine test case
Merge pull request #17 from ckgczarzar/develop

Enhancement