refactor(headers): use String in Access-Control-Allow-Origin header

Access-Control-Allow-Origin origins are URLs but they do not need to
be valid, they should just be compared as strings. So to support
invalid URLs hyper should use a string instead.

closes #526

BREAKING CHANGE: Access-Control-Allow-Origin does no longer use Url

src/error.rs

@@ -3,6 +3,7 @@ use std::error::Error as StdError;
 use std::fmt;
 use std::io::Error as IoError;
 use std::str::Utf8Error;
+use std::string::FromUtf8Error;
 
 use httparse;
 use url;
@@ -127,6 +128,12 @@ impl From<Utf8Error> for Error {
     }
 }
 
+impl From<FromUtf8Error> for Error {
+    fn from(err: FromUtf8Error) -> Error {
+        Utf8(err.utf8_error())
+    }
+}
+
 impl From<httparse::Error> for Error {
     fn from(err: httparse::Error) -> Error {
         match err {