Fix event subscription envelopes

src/usimp/handler/subscribe.rs

@@ -10,7 +10,7 @@ struct Input {}
 
 #[derive(Serialize, Deserialize, Clone)]
 struct Output {
-    event: Option<Event>,
+    events: Vec<Event>,
 }
 
 pub async fn handle(
@@ -45,16 +45,16 @@ async fn subscribe(
                         .send(OutputEnvelope {
                             error: None,
                             request_nr: req_nr,
-                            data: to_value(event).unwrap(),
+                            data: serde_json::json![{"events": [event]}],
                         })
                         .await;
                 }
             });
-            Ok(Output { event: None })
+            Ok(Output { events: vec![] })
         }
         None => {
             if let Some(event) = rx.recv().await {
-                Ok(Output { event: Some(event) })
+                Ok(Output { events: vec![event] })
             } else {
                 Err(Error::new(
                     ErrorKind::SubscriptionError,