Rollup merge of rust-lang#82691 - ehuss:update-books, r=ehuss

Update books

## reference

2 commits in 361367c126290ac17cb4089f8d38fd8b2ac43f98..3b6fe80c205d2a2b5dc8a276192bbce9eeb9e9cf
2021-02-15 09:58:13 -0800 to 2021-02-22 22:09:17 -0800
- Add an extra fn() entry to the variance table in the subtyping chapter (rust-lang/reference#874)
- Turbofish: Explain what the example is of. (rust-lang/reference#966)

## book

28 commits in db5e8a5105aa22979490dce30e33b68d8645761d..0f87daf683ae3de3cb725faecb11b7e7e89f0e5a
2021-02-12 16:58:20 -0500 to 2021-03-01 08:54:04 -0500
- Ohhh the should_panic was for mdbook test. Oops
- Fix bad regex in the update rustc script and regenerate broken output
- Clarify that we only mentioned unwrap_or_else, but haven't explained it
- Add ferris to some listings that don't compile. Fixes rust-lang/book#2598
- Remove fancy quote from a code comment
- Panic now points at our code, not stdlib slice code
- Disable playground on thread::sleep examples
- Disable playground button on listings in ch 12 that use CLI args
- Reword ambiguous sentence. Fixes rust-lang/book#2317.
- Rename shoes_in_my_size to shoes_in_size to be a better example
- Fix visible "ANCHOR: here" in listing 13-21 (rust-lang/book#2628)
- minor clarification about deriving Copy and Clone (rust-lang/book#2627)
- Clarify relationship of trait to mock object
- Fix "message" that should be "method"
- Fix rust-lang/book#2625 (rust-lang/book#2626)
- fix misleading hash claim (rust-lang/book#2621)
- Make link syntax consistent and word wrap
- Added hyperlinks to Appendices
- Use console syntax highlighting in some more places
- Merge remote-tracking branch 'origin/pr/2615'
- Fix broken blockquote
- Update one more bit of output caught by the update rust script
- Update and clarify some text affected by the rand update
- Update lock files and output
- Update error output for changes to chapter 10 listings
- Merge remote-tracking branch 'origin/pr/2542'
- Tweak wording in for loop explanation
- Merge remote-tracking branch 'origin/pr/2460'

## rust-by-example

1 commits in 551cc4bc8394feccea6acd21f86d9a4e1d2271a0..3e0d98790c9126517fa1c604dc3678f396e92a27
2021-02-03 17:12:37 -0300 to 2021-02-25 08:23:10 -0300
- Make flow_control/for/.into_iter() example run (rust-lang/rust-by-example#1415)

## rustc-dev-guide

530 commits in 7adfab4..c431f8c
2020-04-08 08:52:05 +0200 to 2021-02-28 16:35:20 -0500

... Many updates.

## embedded-book

1 commits in 4cf7981696a85c3e633076c6401611bd3f6346c4..a96d096cffe5fa2c84af1b4b61e1492f839bb2e1
2021-02-11 10:55:22 +0000 to 2021-02-17 08:08:52 +0000
- Add note about using more recent openocd interface file. Closes rust-embedded/book#277 and rust-embedded/book#263  (rust-embedded/book#284)