Halloy has insecure file permissions on credential files

Halloy is an IRC application written in Rust. In versions on \*nix and macOS prior to commit f180e41061db393acf65bc99f5c5e7397586d9cb, halloy creates its config directory and files using default umask permissions, which typically results in `0644` on files and `0755` on directories. This allows any local user on the system to read plaintext credentials stored in `config.toml` or referenced `password_file` paths. Commit f180e41061db393acf65bc99f5c5e7397586d9cb patches the issue.