Fix target-feature codegen option syntax in rustc man page.

The man page stated that the list of features was space-separated when
it's actually comma-separated.
adding iterator benches to tree-based maps for comparison purposes
flesh out BTree docs
doc fixups
Rename RELEASES.txt to RELEASES.md. It's markdown.
Update RELEASES.md for 0.12.0
Update AUTHORS.txt for 0.12.0
Update per feedback
Update html_root_url for 0.12.0 release
More relnotes tweaks
librustdoc/html: recognize slices not to nest A tags.

1. A slice of parametrized type, say
   BorrowedRef { ... Vector(Generic(T)) }, is rendered as
   "<a href='primitive.slice.html'>&amp;[T]</a>"
2. A slice of other types, say
   BorrowedRef { ... Vector(int) }, is rendered as
   "<a href='primitive.slice.html'>&amp;[</a>
    <a href='primitive.int.html'>int</a>
    <a href='primitive.slice.html'>]</a>"
3. Other cases, say BorrowedRef { ... int }, are
   rendered as same as before:
   "&<a href='primitive.int.html'>int</a>"

Relevant W3C specs:
- http://www.w3.org/TR/html401/struct/links.html#h-12.2.2
  12.2.2 Nested links are illegal
- http://www.w3.org/TR/html5/text-level-semantics.html#the-a-element
  states A tag must not enclose any "interactive contents"
  which include A tags themselves.
saner parameter order for reallocation functions

Using reallocate(old_ptr, old_size, new_size, align) makes a lot more
sense than reallocate(old_ptr, new_size, align, old_size) and matches up
with the order used by existing platform APIs like mremap.

Closes #17837

[breaking-change]
Clean up the implementations of Bitv and BitvSet.

Functions that add bits now ensure that any unused bits are set to 0.
`into_bitv` sanitizes the nbits of the Bitv/BitvSet it returns by setting the nbits to the current capacity.
Fix a bug with `union_with` and `symmetric_difference` with due to not updating nbits properly
Add test cases to the _with functions
Remove `get_mut_ref`

This is a [breaking-change]. The things you will need to fix are:

1. BitvSet's `unwrap()` has been renamed to `into_bitv`
2. BitvSet's `get_mut_ref()` has been removed. Use `into_bitv()` and `from_bitv()` instead.
librustc: Forbid duplicate name bindings in the same parameter or type
parameter list.

This breaks code like:

    fn f(a: int, a: int) { ... }
    fn g<T,T>(a: T) { ... }

Change this code to not use the same name for a parameter. For example:

    fn f(a: int, b: int) { ... }
    fn g<T,U>(a: T) { ... }

Code like this is *not* affected, since `_` is not an identifier:

    fn f(_: int, _: int) { ... } // OK

Closes #17568.

[breaking-change]
Properly translate boolean statics to be stored as i8

While booleans are represented as i1 in SSA values, LLVM expects them
to be stored/loaded as i8 values. Using i1 as we do now works, but
kills some optimizations, so we should switch to i8, just like we do
everywhere else.

Fixes #16959.
auto merge of #17870 : thestinger/rust/alloc, r=eddyb

Using reallocate(old_ptr, old_size, new_size, align) makes a lot more
sense than reallocate(old_ptr, new_size, align, old_size) and matches up
with the order used by existing platform APIs like mremap.

Closes #17837

[breaking-change]
auto merge of #17875 : dotdash/rust/static_bool, r=alexcrichton

While booleans are represented as i1 in SSA values, LLVM expects them
to be stored/loaded as i8 values. Using i1 as we do now works, but
kills some optimizations, so we should switch to i8, just like we do
everywhere else.

Fixes #16959.
Merge tag '0.12.0'

0.12.0 release
rustc: Reformat check_const with modern style

Remove a bunch of two-space tabs
rustc: Add `const` globals to the language

This change is an implementation of [RFC 69][rfc] which adds a third kind of
global to the language, `const`. This global is most similar to what the old
`static` was, and if you're unsure about what to use then you should use a
`const`.

The semantics of these three kinds of globals are:

* A `const` does not represent a memory location, but only a value. Constants
  are translated as rvalues, which means that their values are directly inlined
  at usage location (similar to a #define in C/C++). Constant values are, well,
  constant, and can not be modified. Any "modification" is actually a
  modification to a local value on the stack rather than the actual constant
  itself.

  Almost all values are allowed inside constants, whether they have interior
  mutability or not. There are a few minor restrictions listed in the RFC, but
  they should in general not come up too often.

* A `static` now always represents a memory location (unconditionally). Any
  references to the same `static` are actually a reference to the same memory
  location. Only values whose types ascribe to `Sync` are allowed in a `static`.
  This restriction is in place because many threads may access a `static`
  concurrently. Lifting this restriction (and allowing unsafe access) is a
  future extension not implemented at this time.

* A `static mut` continues to always represent a memory location. All references
  to a `static mut` continue to be `unsafe`.

This is a large breaking change, and many programs will need to be updated
accordingly. A summary of the breaking changes is:

* Statics may no longer be used in patterns. Statics now always represent a
  memory location, which can sometimes be modified. To fix code, repurpose the
  matched-on-`static` to a `const`.

      static FOO: uint = 4;
      match n {
          FOO => { /* ... */ }
          _ => { /* ... */ }
      }

  change this code to:

      const FOO: uint = 4;
      match n {
          FOO => { /* ... */ }
          _ => { /* ... */ }
      }

* Statics may no longer refer to other statics by value. Due to statics being
  able to change at runtime, allowing them to reference one another could
  possibly lead to confusing semantics. If you are in this situation, use a
  constant initializer instead. Note, however, that statics may reference other
  statics by address, however.

* Statics may no longer be used in constant expressions, such as array lengths.
  This is due to the same restrictions as listed above. Use a `const` instead.

[breaking-change]

[rfc]: https://github.com/rust-lang/rfcs/pull/246