Add support for quoted creds
Merged an equivalent patch, thanks for providing this. I didn't think it was sensible to unquote the username so I removed that logic and changed the parameter to "unquote_password" (vs "unquote_creds").
Addresses https://github.com/coleifer/peewee/issues/1740

- Maintains backwards compatibility by defaulting to current behavior
- Adds flag to all entry points.
- Tests default behavior is preserved but flag provides new behavior.