Vendor dependencies

Let's see how I like this workflow.

vendor/tokio-stream/tests/stream_empty.rs

@@ -0,0 +1,11 @@
+use tokio_stream::{self as stream, Stream, StreamExt};
+
+#[tokio::test]
+async fn basic_usage() {
+    let mut stream = stream::empty::<i32>();
+
+    for _ in 0..2 {
+        assert_eq!(stream.size_hint(), (0, Some(0)));
+        assert_eq!(None, stream.next().await);
+    }
+}