feat(status): add StatusCode::try_from(u16).

This is a temporary function until the `TryFrom` trait stabilizes.

BREAKING CHANGE: Removes the undocumented `from_u16` function. Use
  `StatusCode::try_from` instead.

  Also makes the `status` module private. All imports of
  `hyper::status::StatusCode` should be `hyper::StatusCode`.

src/http/h1/parse.rs

@@ -160,7 +160,8 @@ impl Http1Transaction for ClientTransaction {
                 httparse::Status::Complete(len) => {
                     trace!("Response.try_parse Complete({})", len);
                     let code = res.code.unwrap();
-                    let reason = match StatusCode::from_u16(code).canonical_reason() {
+                    let status = try!(StatusCode::try_from(code).map_err(|_| ::Error::Status));
+                    let reason = match status.canonical_reason() {
                         Some(reason) if reason == res.reason.unwrap() => Cow::Borrowed(reason),
                         _ => Cow::Owned(res.reason.unwrap().to_owned())
                     };

src/http/mod.rs

@@ -89,7 +89,7 @@ impl RawStatus {
     /// Converts this into a StatusCode.
     #[inline]
     pub fn status(&self) -> StatusCode {
-        StatusCode::from_u16(self.0)
+        StatusCode::try_from(self.0).unwrap()
     }
 }