Driver: Reduce logging level in general (#48)

This change reduces many log levels to debug, particularly where errors are likely to be triggered by undocumented Discord messages or by threads exiting in an unpredictable way. This also reduces the task entry/exit messages to `trace`.

This PR has been tested via `cargo make ready`, and by manually inspecting logs at `debug` and `info` levels running `examples/serenity/voice`.

src/driver/tasks/events.rs

@@ -117,5 +117,5 @@ pub(crate) async fn runner(_interconnect: Interconnect, evt_rx: Receiver<EventMe
         }
     }
 
-    info!("Event thread exited.");
+    trace!("Event thread exited.");
 }