(Not `Try` since `QuestionMark` is using that.)

I ignored the code block as I didn't see a way to run the doctest in 2018 -- I noticed the edition guide is also not testing its 2018 code snippits.

This makes it more like `AllSets::{gen,kill}_set`, removes the need for
a bunch of bitset range computations, and removes the need for `Bits`.

It's marginally less efficient, because we have to allocate one bitset
per basic block instead of one large shared bitset, but the difference
is negligible in practice.

The `Buf` vs. non-`Buf` distinction is no longer necessary, and the
nastiest code in this file can be removed.

To minimize this patch, `IdxSet` is made a typedef of `IdxSetBuf`. The
next patch will remove this typedef.

Now that the `Buf` vs. non-`Buf` distinction has been removed, it makes
sense to drop the `Buf` suffix and use the shorter names everywhere.

…ine with other descriptions.

add ticks around a few keywords in other descriptions.

`tool_attributes`, `proc_macro_path_invoc`, partially `proc_macro_gen`

Previously approved in rust-lang#43498 ; update tidy to match.

Implement try block expressions

I noticed that `try` wasn't a keyword yet in Rust 2018, so...

~~Fix​es rust-lang#52604 That was fixed by PR rust-lang#53135
cc rust-lang#31436 rust-lang#50412

Feature gate where clauses on associated type impls

Fixes rust-lang#52913. This doesn't address the core problem, which is tracked by rust-lang#47206. However, it fixes the stable-to-stable regression: you now have to enable `#![feature(generic_associated_types)]` to trigger the weird behaviour.

Stabilize a few secondary macro features

- `tool_attributes` - closes rust-lang#44690
- `proc_macro_path_invoc` - this feature was created due to issues with tool attributes (rust-lang#51277), those issues are now fixed (rust-lang#52841)
- partially `proc_macro_gen` - this feature was created due to issue rust-lang#50504, the issue is now fixed (rust-lang#51952), so proc macros can generate modules. They still can't generate `macro_rules` items though due to unclear hygiene interactions.

… r=nikomatsakis

Merge `IdxSet` and `IdxSetBuf`

Because it simplifies things.

@r? nikomatsakis

…nagisa

Lament the invincibility of the Turbofish

Here a test case is added to ensure that any others attempting to drive the Turbofish to extinction have second thoughts. Previously the [entire test suite would succeed](rust-lang#53511) if generic arguments were accepted without disambiguation, making for [confusing and heartbreaking circumstances](rust-lang/rfcs#2527).

docs: minor stylistic changes to str/string docs

std::string::String.repeat(): slightly rephrase to be more in-line with other descriptions.

add ticks around a few keywords in other descriptions.

…rk-Simulacrum

Update RELEASES.md to include clippy-preview

[Rendered](https://github.com/rust-lang/rust/blob/Aaronepower-patch-1/RELEASES.md#misc)

r? @Mark-Simulacrum

Fix a grammatical mistake in "expected generic arguments" errors

r? @eddyb

…, r=Mark-Simulacrum

tidy: Stop requiring a license header

Previously approved in rust-lang#43498 ; update tidy to match.