Rollup merge of #75168 - ehuss:update-books, r=ehuss

Update books

## reference

7 commits in b329ce37424874ad4db94f829a55807c6e21d2cb..c9b2736a059469043177e1e4ed41a55d7c63ac28
2020-07-20 08:54:08 -0700 to 2020-08-03 03:34:03 -0700
- Fix documented build output path. (rust-lang/reference#870)
- Update token usage table. (rust-lang/reference#868)
- Allow trait inner attributes (rust-lang/reference#864)
- patterns.md - add word "underscore" to _ paragraph (rust-lang/reference#865)
- Drive-by mention unsafe fn closure coercion (rust-lang/reference#802)
- grammar: Change "For awhile" to "For a while" (rust-lang/reference#857)
- Added Unpin to list of Auto Traits (rust-lang/reference#854)

## book

7 commits in a914f2c7e5cdb771fa465de142381a51c53b580e..363293c1c5ce9e84ea3935a5e29ce8624801208a
2020-07-21 09:20:05 -0500 to 2020-08-03 15:56:30 -0500
- replace commas with m-dashes to improve readability of chapter 4.1 (rust-lang/book#2419)
- Update TOML link to official website (rust-lang/book#2411)
- Add github repo link (rust-lang/book#2265)
- Remove the version number entirely so we can stop updating it
- Add link to the `Vec<T>` API documentation (rust-lang/book#2249)
- link to stdlib atomic docs (rust-lang/book#2361)
- mdbook version used is now 0.4.x (rust-lang/book#2410)

## rust-by-example

1 commits in 229c6945a26a53a751ffa4f9cb418388c00029d3..2e9271981adc32613365810f3428334c07095215
2020-07-06 10:13:15 -0300 to 2020-07-27 13:39:16 -0500
- Replaced "princess" with "royal" (rust-lang/rust-by-example#1363)

## embedded-book

1 commits in 94d9ea8460bcbbbfef1877b47cb930260b5849a7..b5256448a2a4c1bec68b93c0847066f92f2ff5a9
2020-07-05 14:17:40 +0000 to 2020-07-24 23:09:29 +0000
- Update c-with-rust.md  (rust-embedded/book#256)