add Debug impl

src/h1/codec.rs

@@ -1,4 +1,5 @@
 #![allow(unused_imports, unused_variables, dead_code)]
+use std::fmt;
 use std::io::{self, Write};
 
 use bytes::{BufMut, Bytes, BytesMut};
@@ -41,6 +42,12 @@ pub struct Codec {
     te: ResponseEncoder,
 }
 
+impl fmt::Debug for Codec {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        write!(f, "h1::Codec({:?})", self.flags)
+    }
+}
+
 impl Codec {
     /// Create HTTP/1 codec.
     ///