refactor(header): make Originheader more allocator friendly

Change the internal representation of Origin to be more allocator
friendly. The internals of the Origin header are now private to allow
changing them in the future.

BREAKING CHANGES:
- Old code that accesses the Origin struct directly will stop working.

src/header/common/origin.rs

@@ -1,4 +1,5 @@
 use header::{Header, Raw, Host};
+use std::borrow::Cow;
 use std::fmt;
 use std::str::FromStr;
 use header::parsing::from_one_raw_str;
@@ -33,19 +34,39 @@ use header::parsing::from_one_raw_str;
 #[derive(Clone, Debug)]
 pub struct Origin {
     /// The scheme, such as http or https
-    pub scheme: String,
+    scheme: Cow<'static,str>,
     /// The host, such as Host{hostname: "hyper.rs".to_owned(), port: None}
-    pub host: Host,
+    host: Host,
 }
 
 impl Origin {
     /// Creates a new `Origin` header.
-    pub fn new<S: Into<String>, H: Into<String>>(scheme: S, hostname: H, port: Option<u16>) -> Origin{
+    pub fn new<S: Into<Cow<'static,str>>, H: Into<Cow<'static,str>>>(scheme: S, hostname: H, port: Option<u16>) -> Origin{
         Origin {
             scheme: scheme.into(),
-            host: Host::new(hostname.into(), port),
+            host: Host::new(hostname, port),
         }
     }
+
+    /// The scheme, such as http or https
+    /// ```
+    /// use hyper::header::Origin;
+    /// let origin = Origin::new("https", "foo.com", Some(443));
+    /// assert_eq!(origin.scheme(), "https");
+    /// ```
+    pub fn scheme(&self) -> &str {
+        &(self.scheme)
+    }
+
+    /// The host, such as Host{hostname: "hyper.rs".to_owned(), port: None}
+    /// ```
+    /// use hyper::header::{Origin,Host};
+    /// let origin = Origin::new("https", "foo.com", Some(443));
+    /// assert_eq!(origin.host(), &Host::new("foo.com", Some(443)));
+    /// ```
+    pub fn host(&self) -> &Host {
+        &(self.host)
+    }
 }
 
 impl Header for Origin {
@@ -77,7 +98,7 @@ impl FromStr for Origin {
 
 
         Ok(Origin{
-            scheme: scheme.to_owned(),
+            scheme: scheme.to_owned().into(),
             host: host
         })
     }