feat(header): implement fmt::Display for several headers

Specifically, `CacheControl`, `Expect`, `Origin`, `Pragma`, `Prefer`,
`PreferenceApplied`, `ReferrerPolicy`, `StrictTransportSecurity`.

src/header/common/cache_control.rs

@@ -65,6 +65,12 @@ impl Header for CacheControl {
     }
 
     fn fmt_header(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        fmt::Display::fmt(self, f)
+    }
+}
+
+impl fmt::Display for CacheControl {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         fmt_comma_delimited(f, &self[..])
     }
 }