[COOK-2047] Filter passwords from log

- Add check for MySQL hex digests; pass these to the log while filtering
  plaintext passwords
- Fix bug in `user`@`host` substring (replace single quotes around @
  with backticks)
Merge pull request #20 from jhx/COOK-2047

[COOK-2047] Filter passwords from log
[COOK-2060] Fix remove backticks when table is nil

- remove backticks from table name when table attribute is nil
- GRANT SELECT ON `*`.`*` TO `some_user`@`%` IDENTIFIED BY 'secret';
  causes MySQL error
- GRANT SELECT ON `*`.* TO `some_user`@`%` IDENTIFIED BY 'secret'; succeeds
Merge pull request #22 from jhx/COOK-2060

[COOK-2060] Fix remove backticks when table is nil
[COOK-2062] Remove backticks from database name

- remove backticks from database name when database_name attribute is nil
Merge pull request #23 from jhx/COOK-2062

[COOK-2062] Remove backticks from database name
release v1.3.8