More Rust updates:

- Some stray deriving -> derive changes
- use::{mod} -> use::{self}
- fmt.write -> fmt.write_str

This does not catch the last case of fmt.write_str in the
Show impl of a Header Item. This will need to be changed
separately.

src/header/shared/encoding.rs

@@ -7,7 +7,7 @@ pub use self::Encoding::{Chunked, Gzip, Deflate, Compress, Identity, EncodingExt
 
 /// A value to represent an encoding used in `Transfer-Encoding`
 /// or `Accept-Encoding` header.
-#[deriving(Clone, PartialEq)]
+#[derive(Clone, PartialEq)]
 pub enum Encoding {
     /// The `chunked` encoding.
     Chunked,