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/libcoretest/char.rs

@@ -210,6 +210,7 @@ fn test_len_utf16() {
     assert!('\u{1f4a9}'.len_utf16() == 2);
 }
 
+#[allow(deprecated)]
 #[test]
 fn test_width() {
     assert_eq!('\x00'.width(false),Some(0));

src/libcoretest/lib.rs

@@ -32,7 +32,7 @@
 extern crate core;
 extern crate test;
 extern crate libc;
-extern crate unicode;
+extern crate rustc_unicode;
 
 mod any;
 mod atomic;