the size is not bytes but objects

and objects were byte arrays (typically 8KB).

limit it to 64, so typically not more than 512kb is used. doesn't change
the max speed when downloading on localhost, and decreases the RSS usage
with slow clients.

src/channel.rs

@@ -19,7 +19,7 @@ type BlockingSender = futures::sink::Wait<Sender>;
 
 
 pub fn stream_tar_in_thread(path: PathBuf) -> Stream {
-    let (writer, stream) = StreamWriter::new(4 * 1024 * 1024);
+    let (writer, stream) = StreamWriter::new(64);
 
     thread::spawn(move || {
         let mut a = tar::Builder::new(writer);