Disable database driver logging or restrict to debug-level only

[atc0005]

Current logging from a pre-v0.1.0 build:

  INFO[0000] mysql2sqlite dev build (https://github.com/atc0005/mysql2sqlite)
  INFO[0000] Connection established to database server at 127.0.0.1:3306
  INFO[0000] Connection established to SQLite database at /var/cache/mysql2sqlite/mailserver.db
  WARN[0000] Fake delay in order to allow for destruction
  INFO[0010] Successfully copied 4 rows from source database table transport_maps
  WARN[0010] Fake delay in order to allow for destruction
[mysql] 2020/09/25 10:33:25 packets.go:122: closing bad idle connection: unexpected read from socket
[mysql] 2020/09/25 10:33:25 connection.go:158: driver: bad connection
  WARN[0020] Transaction rollback complete
 FATAL[0020] failed to prepare row count statement for table access_check_senders: dial tcp 127.0.0.1:3306: connect: connection refused

These lines are useful, but unexpected:

[mysql] 2020/09/25 10:33:25 packets.go:122: closing bad idle connection: unexpected read from socket
[mysql] 2020/09/25 10:33:25 connection.go:158: driver: bad connection

Does the driver offer a way to toggle that output? This output is specific to MySQL, but the concern applies to any database connection used by this application.

[atc0005]

I'm in favor of toggling this on/off via a config file option.

GH-20 would have been easier to debug if I would have had an option wired in to enable debug logging from the MySQL driver. Presumably it would have emitted a warning or debug level message that would have confirmed that I was hitting the configured max connections limit.