* Change `utf8` variable names to `non_ascii` to be more clear, since
ASCII and UTF-8 are compatible.

* Fix `EscapeDefault` struct description to follow the typical iterator
method format with a link to the generating function.

* Add more `escape_default` examples to cover every case mentioned in
the function description itself.

This commit stabilizes the `#![windows_subsystem]` attribute which is a
conservative exposure of the `/SUBSYSTEM` linker flag on Widnows platforms. This
is useful for creating applications as well as console programs.

Closes rust-lang#37499

This reverts commit 2cf686f (rust-lang#40842)

RawFd is a type alias for c_int, which is itself a type alias for i32.
As a result, adding AsRawFd and IntoRawFd impls for RawFd actually adds
them for i32.

As a result, the reverted commit makes this valid:

```
use std::os::unix::io::AsRawFd;

fn arf<T: AsRawFd>(_: T) {}

fn main() {
    arf(32i32)
}
```

Implimenting AsRawFd and IntoRawFd for i32 breaks the promises of both
those traits that their methods return a valid RawFd.

r? @aturon
cc @Mic92 @kamalmarhubi

…d steveklabnik

…ncy, r=steveklabnik

Fix mutex's docs inconsistency

Fixes rust-lang#40176.

r? @steveklabnik
cc @rust-lang/docs

…ystem, r=aturon

rustc: Stabilize the `#![windows_subsystem]` attribute

This commit stabilizes the `#![windows_subsystem]` attribute which is a
conservative exposure of the `/SUBSYSTEM` linker flag on Widnows platforms. This
is useful for creating applications as well as console programs.

Closes rust-lang#37499

… r=alexcrichton

Add a note about overflow for fetch_add/fetch_sub

Fixes rust-lang#40916
Fixes rust-lang#34618

r? @steveklabnik

Improve some docs for VecDeque

r? @GuillaumeGomez

…steveklabnik

Updating the description for BarrierWaitResult rust-lang#29377

Referencing `Barrier`, removing reference to `is_leader`.

API Docs: ascii

Add/update docs for the `ascii` module per rust-lang#29341.

r? @steveklabnik

…xcrichton

Added links to from_utf8 methods in Utf8Error

Referencing  rust-lang#29375. Linked the `from_utf8` methods for both `String` and `str` in the description. Also linked the `u8` to its documentation

…teveklabnik

Added links to types in from_utf8 description

References rust-lang#29375. Link to types mentioned in the documentation for `from_utf8` (`str`, `&[u8`], etc). Paragraphs were reformatted to keep any one line from being excessively long, but are otherwise unchanged.

…teveklabnik

Improve option API docs

Associated Issue: rust-lang#29366

Improve `option` API docs for
* `IntoIter` struct
* `Iter` struct
* `IterMut` struct

r? @steveklabnik

Improve documentation for `std::fs::DirBuilder`

std::thread docs: fix link to current()

…BurntSushi

Fixed typo in doc comments for swap_remove

While reading the Vec docs, I came across the docs for swap_remove. I believe there is a typo in the comment and ```return``` should be ```returns```. This PR fixes this issue.

I also feel that the entire doc comment is a bit of a run-on and could be changed to something along the lines of ```Removes an element from anywhere in the vector and returns it. The vector is mutated and the removed element is replaced by the last element of the vector. ```

Thoughts?

…aturon

Revert "Implement AsRawFd/IntoRawFd for RawFd"

This reverts commit 2cf686f (rust-lang#40842)

RawFd is a type alias for c_int, which is itself a type alias for i32.
As a result, adding AsRawFd and IntoRawFd impls for RawFd actually adds
them for i32.

As a result, the reverted commit makes this valid:

```
use std::os::unix::io::AsRawFd;

fn arf<T: AsRawFd>(_: T) {}

fn main() {
    arf(32i32)
}
```

Implimenting AsRawFd and IntoRawFd for i32 breaks the promises of both
those traits that their methods return a valid RawFd.

r? @aturon
cc @Mic92 @kamalmarhubi