feat: native desktop notifications (experimental) (#59)

* desktop notification by entering `Mode::DONE` for `countdown` and `pomodoro`

* remove redundant `on_done_called` check

* remove build warning (release only)

* log notification errors

* cli arg to enable desktop notifications

* persistant notification settings

* ctrl shortcut

* update changelog

* max timer notification

src/config.rs

@@ -3,7 +3,10 @@ use color_eyre::eyre::{eyre, Result};
 use directories::ProjectDirs;
 use std::fs;
 use std::path::PathBuf;
+
 pub struct Config {
+    // silence `field `log_dir` is never read` the easy way
+    #[cfg_attr(not(debug_assertions), allow(dead_code))]
     pub log_dir: PathBuf,
     pub data_dir: PathBuf,
 }