Improved the tags impl regex
Sort trait bounds.

Closes #6334
doc: make the sentence make more sense
libgetopts: tweak HasHarg/Occur docs.
rustdoc: Use more descriptive description metadata.

This text appears in and improves search results.

cc #12466
rustdoc: Put field instantiation in declaration order.

cc #12466
rustdoc: Emit keywords for all crate pages

cc #12466
rustdoc: Just "stability" instead of "stability dashboard"

The words "stability dashboard" take up too much space on small screens.
stabilize atomics (now atomic)

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]
Fix valgrind.h for Win64.
_WIN32 is defined for 64-bit builds as well, so test for _WIN64 first.
Ensure that Registers struct is 16-byte aligned on x86_64.
This is important when building with --disable-jemalloc: unlike jemalloc,  msvcrt does not align on 16 bytes unless asked to.
libnative should not mess with stack limits in the TIB.  Only libgreen has a legitimate need to set them.
Use mingw64 target spelling.
Use gcc for cross-build linking, not g++.
Fix crash in OsRng when compiling with -O.
Update LLVM
Implement unwinding for Win64.
The original trick used to trigger unwinds would not work with GCC's implementation of SEH, so I had to invent a new one: rust_try now consists of two routines: the outer one, whose handler triggers unwinds, and the inner one, that stops unwinds by having a landing pad that swallows exceptions and passes them on to the outer routine via a normal return.
Fix tests.
Remove obsolete stack growth tests
Remove references to `~[]` in core::kinds::marker docs.