This is useful to build os abstraction like the nix crate does.
It allows to define functions, which accepts generic arguments
of data structures convertible to RawFd, including RawFd itself.
For example:

  fn write<FD: AsRawFd>(fd: FD, buf: &[u8]) -> Result<usize>

instead of:

  fn write(fd: RawFd, buf: &[u8]) -> Result<usize>
  write(foo.as_raw_fd(), buf);

Fixes rust-lang#40724

Remove feature `rustdoc`.

add link to specialization's tracking issue

When in debug_assertions=true mode, the function consume_body lacks some debug output, which makes it harder to follow the control flow. This commit adds this needed debug.

When making a forwarding wrapper we must in general forward all methods,
so that we use the type's own `lt` for example instead of the default.

Example important case: f32's partial_cmp does several operations but
its lt is a primitive.

This change reduces duplication by linking the documentation for
`writeln!` to `write!`. It also restructures the `write!` documentation
to read in a more logical manner.

Updates rust-lang#29329, rust-lang#29381

Add a tidy lint that checks for...

* Unstable Book sections with no corresponding SUMMARY.md links
* unstable features that don't have Unstable Book sections
* Unstable Book sections that don't have corresponding unstable features

…teveklabnik

Sync all unstable features with Unstable Book; add tidy lint.

Add a tidy lint that checks for...

* Unstable Book sections with no corresponding SUMMARY.md links
* unstable features that don't have Unstable Book sections
* Unstable Book sections that don't have corresponding unstable features

Implement AsRawFd/IntoRawFd for RawFd

This is useful to build os abstraction like the nix crate does.
It allows to define functions, which accepts generic arguments
of data structures convertible to RawFd, including RawFd itself.
For example:

```
fn write<FD: AsRawFd>(fd: FD, buf: &[u8]) -> Result<usize>
write(file, buf);
```
instead of:
```
fn write(fd: RawFd, buf: &[u8]) -> Result<usize>
write(file.as_raw_fd(), buf);
```

cc @kamalmarhubi

Improve os::linux documentation (rust-lang#29367)

Improve `os::linux` documentation according to rust-lang#29367

r? @steveklabnik

…GuillaumeGomez

Make the rustdoc sidebar white on `src` pages

Fixes rust-lang#40724

…=alexcrichton

Remove unused feature from error index generator

Remove feature `rustdoc`.

Add example to std::process::abort

This is a first step in order to complete this issue: rust-lang#29370
I submitted this PR with the help of @steveklabnik More info here: rust-lang#29370 (comment)

It's my first PR on Rust, I'm learning how to contribute: Should I ping someone? I will post another PR with a more complicated example soon, I prefer send it separately (cause maybe I made some mistakes).

Add missing link in unstable-book

add link to specialization's tracking issue

adding debug in consume_body function

When in debug_assertions=true mode, the function consume_body lacks some debug output, which makes it harder to follow the control flow. This commit adds this needed debug.

Implement all PartialOrd methods for Reverse

When making a forwarding wrapper we must in general forward all methods,
so that we use the type's own `lt` for example instead of the default.

Example important case: f32's partial_cmp does several operations but
its lt is a primitive.

Follow up on rust-lang#40720

…s, r=steveklabnik

Improve the docs for the write and writeln macros

This change reduces duplication by linking the documentation for
`writeln!` to `write!`. It also restructures the `write!` documentation
to read in a more logical manner (I hope; feedback would be welcome).

Updates rust-lang#29329, rust-lang#29381