Implemented a typed Authorization header

An Authorization header contains a Scheme. If you have no real scheme,
you can use String as your scheme (Authorization<String>).

This includes the `Basic` scheme built-in.

src/header/common/util.rs

@@ -9,7 +9,7 @@ pub fn from_one_raw_str<T: FromStr>(raw: &[Vec<u8>]) -> Option<T> {
         return None;
     }
     // we JUST checked that raw.len() == 1, so raw[0] WILL exist.
-    match from_utf8(unsafe { raw.as_slice().unsafe_get(0).as_slice() }) {
+    match from_utf8(unsafe { raw[].unsafe_get(0)[] }) {
         Some(s) => FromStr::from_str(s),
         None => None
     }