Add standard traits to Bitrate.

src/session.rs

@@ -28,7 +28,7 @@ use version;
 
 use stream;
 
-#[derive(Clone, Copy)]
+#[derive(Clone, Copy, Debug, PartialOrd, Ord, PartialEq, Eq)]
 pub enum Bitrate {
     Bitrate96,
     Bitrate160,