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.