deprecate Unicode functions that will be moved to crates.io

This patch
1. renames libunicode to librustc_unicode,
2. deprecates several pieces of libunicode (see below), and
3. removes references to deprecated functions from
   librustc_driver and libsyntax. This may change pretty-printed
   output from these modules in cases involving wide or combining
   characters used in filenames, identifiers, etc.

The following functions are marked deprecated:

1. char.width() and str.width():
   --> use unicode-width crate

2. str.graphemes() and str.grapheme_indices():
   --> use unicode-segmentation crate

3. str.nfd_chars(), str.nfkd_chars(), str.nfc_chars(), str.nfkc_chars(),
   char.compose(), char.decompose_canonical(), char.decompose_compatible(),
   char.canonical_combining_class():
   --> use unicode-normalization crate

src/libserialize/lib.rs

@@ -41,7 +41,7 @@ Core encoding and decoding interfaces.
 #[cfg(test)] extern crate test;
 #[macro_use] extern crate log;
 
-extern crate unicode;
+extern crate rustc_unicode;
 extern crate collections;
 
 pub use self::serialize::{Decoder, Encoder, Decodable, Encodable,