Complete skeleton dispatcher

- Complete the dispatcher for the 'introducer' and 'local' command. This
  is currently only a skeleton.
- The 'introducer list' command is added.

src/main.rs

@@ -42,12 +42,8 @@ async fn main() {
 
     let config_container: HuskConfigContainer = Arc::new(Mutex::new(husk_config));
 
-    match commands::dispatch(args, config_container).await {
-        Ok(_) => {
-            println!("exiting...");
-        },
-        Err(e) => {
-            println!("exit with {:?}", e);
-        }
+    if let Err(e) = commands::dispatch(args, config_container).await {
+        eprintln!("exit with {:?}", e);
+        // XXX: actually return an error code
     }
 }