Implement Show for DList
Implement ToSource and ToToken for ast::Arg

This makes ast::Arg usable in the quote_ macros.

Please note that this commit doesn't include a regression test. There
are tests that use the quote macros, but all of them are ignored. Due to
that, there is no obvious (to me) way to test this.

Since this change is absolutely trivial and only hooks up an additional
type to existing infrastructure (which presumably is tested elsewhere),
I concluded it's not worth the effort to follow up on this.
relicense shootout-regex-dna.rs

Part of #14248

The authors are @pcwalton and @BurntSushi, and we have their agreement.
Implement Show for SmallIntMap
rustdoc: More selectively remove execute links

Closes #14723
auto merge of #14730 : alexcrichton/rust/issue-14723, r=cmr

Closes #14723
auto merge of #14722 : hannobraun/rust/quote-args, r=alexcrichton

The need for this came up while I worked on a procedural macro that parses an argument and adds the same argument to a generated function.
auto merge of #14725 : aochagavia/rust/show, r=alexcrichton
Fix PartialEq documentation with regards to floats

It is in fact the case that `NaN != NaN`. The true relations for
compareQuietNotEqual are LT, GT *and* UN.

I also rephrased the docs for PartialOrd since floats are not the only
types which are not totally ordered.
Clarify restrictions on ne

I can't think of any sane cases where this restriction would not hold,
and the standard library seems to assume it pretty much everywhere.
auto merge of #14733 : sfackler/rust/partial-eq-nan-docs, r=alexcrichton

It is in fact the case that `NaN != NaN`. The true relations for
compareQuietNotEqual are LT, GT *and* UN.

I also rephrased the docs for PartialOrd since floats are not the only
types which are not totally ordered.
Add visit_attribute to Visitor, use it for unused_attribute

The lint was missing a *lot* of cases previously.
Remove the attribute_usage lint

It has been superseded by the unused_attribute lint.

[breaking change]
Improve error message for range in match

Range allows char and numeric types, but previous error message
mentioned only numeric types.
Add back hint for crate level attributes
Remove unused name_str_pair method
auto merge of #14743 : Sawyer47/rust/range-msg, r=huonw

Range allows char and numeric types, but previous error message
mentioned only numeric types.
std::io: expand the oneshot/periodic docs.

Examples!

Fixes #14714.
auto merge of #14728 : TeXitoi/rust/relicense-shootout-regex-dna, r=brson

Part of #14248

The authors are @pcwalton and @BurntSushi, and we have their agreement.

@brson OK?
auto merge of #14741 : sfackler/rust/visit-attr, r=alexcrichton

The lint was missing a *lot* of cases previously.