Introduce syntax for lifetime bounds like `'b:'a`, meaning `'b outlives 'a`. Syntax currently does nothing but is needed for full fix to #5763. To use this syntax, the issue_5763_bootstrap feature guard is required.

meaning `'b outlives 'a`. Syntax currently does nothing but is needed for full
fix to #5763. To use this syntax, the issue_5763_bootstrap feature guard is
required.

Signature for `from_digit` in `Char` wasn't using `Self` so there was no way to use this method

AST refactoring: merge PatWild and PatWildMulti into one variant with a flag

This replaces many instances chars being casted to u8 with byte literals.

Simplifying the code of methods: `nth`, `fold`, `rposition`, and iterators: `Filter`, `FilterMap`, `SkipWhile`.

```
before
test iter::bench_multiple_take      ... bench:        15 ns/iter (+/- 0)
test iter::bench_rposition          ... bench:       349 ns/iter (+/- 94)
test iter::bench_skip_while         ... bench:       158 ns/iter (+/- 6)

after
test iter::bench_multiple_take      ... bench:        15 ns/iter (+/- 0)
test iter::bench_rposition          ... bench:       314 ns/iter (+/- 2)
test iter::bench_skip_while         ... bench:       107 ns/iter (+/- 0)
```
@koalazen has the code for `Skip`.

Once #16011 is fixed, `min_max` could use a for loop.

 Closes #6334

Previously the implementation detection regex would detect
`impl fmt::Show for MyStruct` as `fmt`. Now it will be detected as
`fmt::Show for MyStruct`. Implementations such as `impl MyStruct` will
still be detected as `MyStruct`.

Simplifying the code of methods: nth, fold, rposition
and iterators: Filter, FilterMap, SkipWhile
Adding basic benchmarks

… to separate text from the edge of the newly added background.

This commit stabilizes the `std::sync::atomics` module, renaming it to
`std::sync::atomic` to match library precedent elsewhere, and tightening
up behavior around incorrect memory ordering annotations.

The vast majority of the module is now `stable`. However, the
`AtomicOption` type has been deprecated, since it is essentially unused
and is not truly a primitive atomic type. It will eventually be replaced
by a higher-level abstraction like MVars.

Due to deprecations, this is a:

[breaking-change]

This teach rustdoc to add `<meta name="description">` and `<meta name="keywords">` tags to crate docs. Description is important for search engines because they display it as the page description. Keywords are less useful but still generally recommended.

This also changes the "stability dashboard" link to just say "stability", because the current link takes up a lot of space.

cc https://github.com/rust-lang/rust/issues/12466

For a good measure, implemented target_record_stack_bounds for 32-bit Windows as well.