refactor(headers): add deref of Etag to EntityTag

Author: hugoduncan

src/header/common/etag.rs

@@ -11,6 +11,8 @@ use header::parsing::from_one_raw_str;
 #[derive(Clone, PartialEq, Debug)]
 pub struct Etag(pub EntityTag);
 
+deref!(Etag => EntityTag);
+
 impl Header for Etag {
     fn header_name() -> &'static str {
         "Etag"