feat(headers): adds Accept

Moved utils to shared/. Added quality_value.

src/header/common/transfer_encoding.rs

@@ -1,7 +1,7 @@
 use header::{Header, HeaderFormat};
 use std::fmt;
 use std::str::FromStr;
-use super::util::{from_comma_delimited, fmt_comma_delimited};
+use header::shared::util::{from_comma_delimited, fmt_comma_delimited};
 
 use self::Encoding::{Chunked, Gzip, Deflate, Compress, EncodingExt};