The functions return a reference to a new object and do not modify in-place
as the following code shows:
````
let s = String::from("   hello   ");
s.trim();
assert_eq!(s, "   hello   ");
````

The new reference should be bound to a variable as now indicated by #[must_use].

trimmed string is returned as a slice instead of a new allocation

Co-Authored-By: matthiaskrgr <matthias.krueger@famsik.de>

mark str::string::String.trim.* functions as #[must_use].

The functions return a reference to a new object and do not modify in-place
as the following code shows:
````
let s = String::from("   hello   ");
s.trim();
assert_eq!(s, "   hello   ");
````

The new reference should be bound to a variable as now indicated by #[must_use].

…mulacrum

use `SOURCE_DATE_EPOCH` for man page time if set

Fixes rust-lang#57776.

…alexcrichton

Introduce into_raw_non_null on Rc and Arc

None

…ichton

override `VecDeque`'s `Iter::try_fold`

This should improve performance (wherever it is used), but I haven't found the time to benchmark it yet.