Vendor dependencies

Let's see how I like this workflow.

vendor/bytes/tests/test_iter.rs

@@ -0,0 +1,21 @@
+#![warn(rust_2018_idioms)]
+
+use bytes::Bytes;
+
+#[test]
+fn iter_len() {
+    let buf = Bytes::from_static(b"hello world");
+    let iter = buf.iter();
+
+    assert_eq!(iter.size_hint(), (11, Some(11)));
+    assert_eq!(iter.len(), 11);
+}
+
+#[test]
+fn empty_iter_len() {
+    let buf = Bytes::from_static(b"");
+    let iter = buf.iter();
+
+    assert_eq!(iter.size_hint(), (0, Some(0)));
+    assert_eq!(iter.len(), 0);
+}