std: Stabilize the hash module

This commit is an implementation of [RFC 823][rfc] which is another pass over
the `std::hash` module for stabilization. The contents of the module were not
entirely marked stable, but some portions which remained quite similar to the
previous incarnation are now marked `#[stable]`. Specifically:

[rfc]: https://github.com/rust-lang/rfcs/blob/master/text/0823-hash-simplification.md

* `std::hash` is now stable (the name)
* `Hash` is now stable
* `Hash::hash` is now stable
* `Hasher` is now stable
* `SipHasher` is now stable
* `SipHasher::new` and `new_with_keys` are now stable
* `Hasher for SipHasher` is now stable
* Many `Hash` implementations are now stable

All other portions of the `hash` module remain `#[unstable]` as they are less
commonly used and were recently redesigned.

This commit is a breaking change due to the modifications to the `std::hash` API
and more details can be found on the [RFC][rfc].

Closes #22467
[breaking-change]

src/test/bench/core-set.rs

@@ -18,7 +18,6 @@ extern crate rand;
 use std::collections::BTreeSet;
 use std::collections::BitvSet;
 use std::collections::HashSet;
-use std::collections::hash_map::Hasher;
 use std::hash::Hash;
 use std::env;
 use std::time::Duration;
@@ -43,7 +42,7 @@ trait MutableSet<T> {
     fn contains(&self, k: &T) -> bool;
 }
 
-impl<T: Hash<Hasher> + Eq> MutableSet<T> for HashSet<T> {
+impl<T: Hash + Eq> MutableSet<T> for HashSet<T> {
     fn insert(&mut self, k: T) { self.insert(k); }
     fn remove(&mut self, k: &T) -> bool { self.remove(k) }
     fn contains(&self, k: &T) -> bool { self.contains(k) }

src/test/compile-fail/issue-21160.rs

@@ -16,6 +16,6 @@ impl Bar {
 
 #[derive(Hash)]
 struct Foo(Bar);
-//~^ error: the trait `core::hash::Hash<_>` is not implemented for the type `Bar`
+//~^ error: the trait `core::hash::Hash` is not implemented for the type `Bar`
 
 fn main() {}

src/test/run-pass/deriving-hash.rs

@@ -17,7 +17,7 @@ struct Person {
     phone: uint,
 }
 
-fn hash<T: Hash<SipHasher>>(t: &T) -> u64 {
+fn hash<T: Hash>(t: &T) -> u64 {
     std::hash::hash::<T, SipHasher>(t)
 }
 

src/test/run-pass/deriving-meta-multiple.rs

@@ -20,7 +20,7 @@ struct Foo {
     baz: int
 }
 
-fn hash<T: Hash<SipHasher>>(_t: &T) {}
+fn hash<T: Hash>(_t: &T) {}
 
 pub fn main() {
     let a = Foo {bar: 4, baz: -3};

src/test/run-pass/deriving-meta.rs

@@ -17,7 +17,7 @@ struct Foo {
     baz: int
 }
 
-fn hash<T: Hash<SipHasher>>(_t: &T) {}
+fn hash<T: Hash>(_t: &T) {}
 
 pub fn main() {
     let a = Foo {bar: 4, baz: -3};