Readme clashes with Backend trait contract

[urkle]

The Backend trait contract returns Option<&str> in version 2.0, however the README shows the example of the RemoveI18n that returns Option instead.

Currently I'm trying to create a "reloadable backend". where I can setup a watcher via the Notify create to reload the translations from disk. However I am running into issues due to the contract change of Backend as I am unable to return a reference to a string.

struct ReloadableBackend {
    translations: Arc<RwLock<HashMap<String, HashMap<String, String>>>>,
}

impl Backend for ReloadableBackend {
   fn available_locales(&self) -> Vec<&str> {
        let l = self.i18n.read();
        if let Ok(h) = l {
            let mut locales = h.keys().map(|k| k.as_str()).collect::<Vec<_>>();
            locales.sort();
            locales // Error cannot return value referencing local variable `h` [E0515] returns a value referencing data owned by the current function
        } else {
            Vec::new()
        }
    }

    fn translate(&self, locale: &str, key: &str) -> Option<&'_ str> {
        let l = self.i18n.read();
        if let Ok(h) = l {
            return h
                .get(locale)
                .and_then(|trs| trs.get(key))
                .and_then(|k| Some(k.as_str())); // cannot return value referencing local variable `h` [E0515] returns a value referencing data owned by the current function
        } else {
            None
        }
    }
}

This, of course, makes perfect sense since it has to return a reference from the locked data in the Arc.

If the contract were still returning String then this would not be an issue as I could just return a cloned string and move on.