Add support for multiple targets and live-reload.

src/listener.rs

@@ -1,7 +1,9 @@
 use crate::shutdown::Shutdown;
+use std::sync::Arc;
+use tokio::sync::RwLock;
 
 pub(crate) struct Listener {
    pub(crate) shutdown: Shutdown,
    pub(crate) source: String,
-   pub(crate) target: String,
+   pub(crate) targets: Arc<RwLock<Vec<String>>>,
 }