StreamRef sends RST_STREAM on drop (#109)

This PR modifies the `Drop` implementation for `StreamRef` to reset the underlying stream if it is the last reference to that stream. Since both `Stream` and `Body` are internally just a `StreamRef`, this means they will both reset the stream on drop; thus, this closes #100.

The assertion that the store no longer contains the dropped stream ID at the end of the `Drop` method  had to be removed, as the stream has to be reset from inside of a `transition` block (which now manages releasing that ID for us), and the `transition` closure moves the value of `stream`, making the assertion no longer possible.

Modifications to some of the tests in `flow_control.rs` were also necessary, in order to prevent `StreamRef`s from being dropped too early.

examples/server.rs

@@ -27,7 +27,6 @@ pub fn main() {
     let server = listener.incoming().for_each(move |(socket, _)| {
         // let socket = io_dump::Dump::to_stdout(socket);
 
-
         let connection = Server::handshake(socket)
             .and_then(|conn| {
                 println!("H2 connection bound");
@@ -35,6 +34,7 @@ pub fn main() {
                 conn.for_each(|(request, mut stream)| {
                     println!("GOT request: {:?}", request);
 
+
                     let response = Response::builder().status(StatusCode::OK).body(()).unwrap();
 
                     if let Err(e) = stream.send_response(response, false) {
@@ -47,12 +47,11 @@ pub fn main() {
                     }
 
                     Ok(())
-                }).and_then(|_| {
-                        println!(
-                            "~~~~~~~~~~~~~~~~~~~~~~~~~~~ H2 connection CLOSE !!!!!! ~~~~~~~~~~~"
-                        );
-                        Ok(())
-                    })
+                })
+            })
+            .and_then(|_| {
+                println!("~~~~~~~~~~~~~~~~~~~~~~~~~~~ H2 connection CLOSE !!!!!! ~~~~~~~~~~~");
+                Ok(())
             })
             .then(|res| {
                 if let Err(e) = res {