Rust 0.4.0

* ~2000 changes, numerous bugfixes

* Syntax

* All keywords are now strict and may not be used as identifiers anywhere

* Keyword removal: 'again', 'import', 'check', 'new', 'owned', 'send',

'of', 'with', 'to', 'class'.

* Classes are replaced with simpler structs

* Explicit method self types

* ret became return and alt became match

* import is now use; use is now extern mod

* extern mod { ... } is now extern { ... }

* use mod is the recommended way to import modules

* pub and priv replace deprecated export lists

* The syntax of match pattern arms now uses fat arrow (=>)

* main no longer accepts an args vector; use os::args instead

* Semantics

* Trait implementations are now coherent, ala Haskell typeclasses

* Trait methods may be static

* Argument modes are deprecated

* Borrowed pointers are much more mature and recommended for use

* Strings and vectors in the static region are stored in constant memory

* Typestate was removed

* Resolution rewritten to be more reliable

* Support for 'dual-mode' data structures (freezing and thawing)

* Libraries

* Most binary operators can now be overloaded via the traits in

core::ops'

* std::net::url for representing URLs

* Sendable hash maps in core::send_map

* core::task' gained a (currently unsafe) task-local storage API

* Concurrency

* An efficient new intertask communication primitive called the pipe,

along with a number of higher-level channel types, in core::pipes

* std::arc, an atomically reference counted, immutable, shared memory

type

* std::sync`, various exotic synchronization tools based on arcs and pipes

* Futures are now based on pipes and sendable

* More robust linked task failure

* Improved task builder API

* Other

* Improved error reporting

* Preliminary JIT support

* Preliminary work on precise GC

* Extensive architectural improvements to rustc

* Begun a transition away from buggy C++-based reflection (shape) code to

Rust-based (visitor) code

* All hash functions and tables converted to secure, randomized SipHash