Original headline of SplitWhitespace's description is more descriptive as to what it contains and iterates over.

fixed some clippy warnings in libcollections

Some markdown fixes, a few readability improvements, but mostly trivial stuff.

…eklabnik

Add missing urls in ptr docs

r? @rust-lang/docs

Make overlapping_inherent_impls lint a hard error

Closes rust-lang#36889.

Add helpful hint in io docs about how ? is not allowed in main()

This is my effort to help alleviate the confusion caused by the error message:
```rust
error[E0277]: the trait bound `(): std::ops::Carrier` is not satisfied
  --> hello_world.rs:72:5
   |
72 |     io::stdin().read_line(&mut d_input)?;
   |     ------------------------------------
   |     |
   |     the trait `std::ops::Carrier` is not implemented for `()`
   |     in this macro invocation
   |
   = note: required by `std::ops::Carrier::from_error`

error: aborting due to previous error
```
This has been discussed at length in rust-lang#35946, but I figured it would be helpful to mention in the docs.
Reading user input is one of the first things beginners will look up in the docs, so my thinking was they'd see this warning here and not have to deal with the [tricky error message](https://blog.rust-lang.org/2017/03/02/lang-ergonomics.html).

If you think this isn't the right place to put this in the docs, that's understandable, I'm open to suggestions for putting it elsewhere or removing it entirely.

Adding links for Atomics docs rust-lang#29377

r? @steveklabnik

This should be good for `std::sync::atomic`. The other pages still need more (examples, etc.).

…r=steveklabnik

Modify str Structs descriptions

References rust-lang#29375. Modified descriptions of multiple structs to be more in line with structs found under [`std::iter`](https://doc.rust-lang.org/std/iter/#structs), such as [`Chain`](https://doc.rust-lang.org/std/iter/struct.Chain.html) and [`Enumerate`](https://doc.rust-lang.org/std/iter/struct.Enumerate.html)

…excrichton

Test sort algorithms using a random cmp function

This ensures that sorting using a broken comparison function doesn't panic nor fail in some other way (especially not segfault).

r? @alexcrichton