refactor(http): add status() methods to RawStatus and ResponseHead

This lets us convert RawStatus to StatusCode in Response without having to address the tuple index
directly.

src/http/mod.rs

@@ -71,10 +71,26 @@ impl<S> MessageHead<S> {
     }
 }
 
+impl ResponseHead {
+    /// Converts this head's RawStatus into a StatusCode.
+    #[inline]
+    pub fn status(&self) -> StatusCode {
+        self.subject.status()
+    }
+}
+
 /// The raw status code and reason-phrase.
 #[derive(Clone, PartialEq, Debug)]
 pub struct RawStatus(pub u16, pub Cow<'static, str>);
 
+impl RawStatus {
+    /// Converts this into a StatusCode.
+    #[inline]
+    pub fn status(&self) -> StatusCode {
+        StatusCode::from_u16(self.0)
+    }
+}
+
 impl fmt::Display for RawStatus {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         write!(f, "{} {}", self.0, self.1)