Improved the tags impl regex
Sort trait bounds.

Closes #6334
collections, unicode: Add support for NFC and NFKC
Guide: testing
Library changes for RFC #43
Add two helper functions for dealing with OwnedPtr paths
Implement RFC #43

Remove the ability of the borrow checker to determine that repeated
dereferences of a Box<T> refer to the same memory object. This will
usually require one of two workarounds:

1) The interior of a Box<T> will sometimes need to be moved / borrowed
into a temporary before moving / borrowing individual derived paths.

2) A `ref x` pattern will have to be replaced with a `box ref x`
pattern.

Fixes #16094.

[breaking-change]
Add a new test for borrow checker Box<T> behavior
Add comment about speed in FAQ.

Fixes #11174.
fix variable name in tutorial
rustrt: Make begin_unwind take a single file/line pointer

Smaller text size.
Modify failure lang items to take less pointers.

Divide-by-zero before:

```
        leaq    "str\"str\"(1762)"(%rip), %rax
        movq    %rax, 16(%rsp)
        movq    $27, 24(%rsp)
        leaq    "str\"str\"(1542)"(%rip), %rax
        movq    %rax, (%rsp)
        movq    $19, 8(%rsp)
        leaq    16(%rsp), %rdi
        leaq    (%rsp), %rsi
        movl    $32, %edx
        callq   _ZN7failure5fail_20hc04408f955ce60aaqWjE@PLT
```

After:

```
        leaq    .Lconst(%rip), %rdi
        callq   _ZN7failure5fail_20haf918a97c8f7f2bfqWjE@PLT
```

Bounds check before:

```
        leaq    "str\"str\"(1542)"(%rip), %rax
        movq    %rax, 8(%rsp)
        movq    $19, 16(%rsp)
        leaq    8(%rsp), %rdi
        movl    $38, %esi
        movl    $1, %edx
        movl    $1, %ecx
        callq   _ZN7failure17fail_bounds_check20hf4bc3c69e96caf41RXjE@PLT
```

Bounds check after:

```
        leaq    .Lconst2(%rip), %rdi
        movl    $1, %esi
        movl    $1, %edx
        callq   _ZN7failure17fail_bounds_check20h5267276a537a7de22XjE@PLT
```

Size before:

21277995 librustc-4e7c5e5c.s

```
text       data
12554881   6089335
```

Size after:

21247617 librustc-4e7c5e5c.so

```
text       data
12518497   6095748
```
core: Add #[inline(never)] to failure functions

For consistency, just because `fail_` has it.
core: Fix failure doc comment
Fix deprecation commment on `core::cmp::lexical_ordering`
fix formatting in pointer guide table
remove serialize::ebml, add librbml

Our implementation of ebml has diverged from the standard in order
to better serve the needs of the compiler, so it doesn't make much
sense to call what we have ebml anyore. Furthermore, our implementation
is pretty crufty, and should eventually be rewritten into a format
that better suits the needs of the compiler. This patch factors out
serialize::ebml into librbml, otherwise known as the Really Bad
Markup Language. This is a stopgap library that shouldn't be used
by end users, and will eventually be replaced by something better.

[breaking-change]
Move SeekableMemWriter into librbml
Fix heading levels in pointer guide
rustrt: Don't conditionally init the at_exit QUEUE

This initialization should happen unconditionally, but the rtassert! macro is
gated on the ENFORCE_SANITY define

Closes #16106