Rollup merge of rust-lang#87503 - ehuss:update-books, r=ehuss

Update books

## nomicon

1 commits in 7a13537f96af4b9b8e3ea296d6e5c3c7ab72ce9f..f51734eb5566c826b471977747ea3d7d6915bbe9
2021-07-05 23:34:47 -0400 to 2021-07-23 18:24:35 +0900
- Add cloning example for dot operator behaviour (rust-lang/nomicon#292)

## reference

3 commits in 82d75cf423e4a7824fb36e73ccb18519d6900610..3b7be075af5d6e402a18efff672a8a265b4596fd
2021-07-15 06:49:08 -0700 to 2021-07-26 13:20:11 -0700
- Fix typos + grammar (rust-lang/reference#1037)
- Expand on Unicode identifiers. (rust-lang/reference#1022)
- Remove incorrect apostrophe (rust-lang/reference#1076)

## book

17 commits in eac55314210519238652f12b30fec9daea61f7fe..a07036f864b37896b31eb996cd7aedb489f69a1f
2021-07-19 11:08:01 -0400 to 2021-07-26 20:19:46 -0400
- Set expectations a bit more realistically
- Snapshot of chapter 4 for nostarch
- A few small wording tweaks in ch 4
- Clarify that it's not stack/heap exactly that matters for copy/non copy, fixes rust-lang/book#2799
- Clarify a detail around move. Fixes rust-lang/book#2413.
- Clarify places that changed because of NLL. Fixes rust-lang/book#1939.
- nostarch ch3
- Small edits to chapter 3
-  (rust-lang/book#2797)
- Update ch03-03-how-functions-work.md: Pervasive -> Prevalent. (rust-lang/book#2796)
- Address loop labels and continue. Fixes rust-lang/book#1392.
- Clarify behavior of integer division. Fixes rust-lang/book#2248.
- Demonstrate how scope interacts with shadowing
- Add another cross-reference to the new unit type introduction
- Introduce the unit type with tuples. Fixes rust-lang/book#1933.
- Reword sentence to not have numbers separated only by a comma
- Link directly to other installation page. Fixes rust-lang/book#1609

## rust-by-example

1 commits in 1db6bb483cc87ad3b424d9aba764fe622960a1be..0dc9cd4e89f00cb5230f120e1a083916386e422b
2021-07-15 06:17:42 -0300 to 2021-07-23 09:14:27 -0300
- Grammatical mistake: Comparison as ... as the (rust-lang/rust-by-example#1453)

## rustc-dev-guide

2 commits in 93422c2..09343d6
2021-07-13 12:45:58 -0400 to 2021-07-26 00:37:28 +0200
- Fix typo in building/bootstrapping.md (rust-lang/rustc-dev-guide#1175)
- Link directly to stabilization report comments (rust-lang/rustc-dev-guide#1173)

## edition-guide

4 commits in af696ce8ea526445590ae0ca66a8128d2a95a69a..3710b0cae783d0bcd2b42452a63b081473f5970a
2021-07-20 11:38:03 -0400 to 2021-07-26 11:34:46 -0700
- Add more consistent headings and add a migration section to reserving-syntax (rust-lang/edition-guide#263)
- reserving-syntax.md: Expand and add detail (rust-lang/edition-guide#249)
- Fix typo in or-patterns section (rust-lang/edition-guide#262)
- Fix typo (rust-lang/edition-guide#261)

Author: JohnTitor