Rollup merge of #67962 - ehuss:update-books, r=ehuss

Update books

## nomicon

1 commits in 8be35b201f9cf0a4c3fcc96c83ac21671dcf3112..3e6e1001dc6e095dbd5c88005e80969f60e384e1
2019-12-01 13:02:12 -0500 to 2019-12-14 22:08:52 +0000
- Remove mention of contravariance possibly getting scrapped (rust-lang/nomicon#177)

## reference

4 commits in d8dfe1b..e115753
2019-12-14 21:04:58 +0100 to 2019-12-22 13:13:14 +0100
- Fix typo in macros-by-example.md (rust-lang/reference#733)
- Remove `extern` from exception list (rust-lang/reference#732)
- Added clearification that closures are refered to lambdas (rust-lang/reference#731)
- abi.md: clarify #[used] and linking (rust-lang/reference#712)

## book

2 commits in ef8bb568035ded8ddfa30a9309026638cc3c8136..5c5cfd2e94cd42632798d9bd3d1116133e128ac9
2019-11-28 11:00:04 -0600 to 2019-12-16 09:27:21 -0600
- document new --show-output option in ch 11-2 (Rust >= 1.39) (rust-lang/book#2065)
- Fix sentence in ch07 (rust-lang/book#2183)

## rust-by-example

3 commits in b7ac1bc76b7d02a43c83b3a931d226f708aa1ff4..1d59403cb5269c190cc52a95584ecc280345495a
2019-12-02 11:38:43 -0300 to 2019-12-27 08:27:05 -0300
- Enable section-folding of table of content (rust-lang/rust-by-example#1290)
- Remove unnecessary lifetime annotation (rust-lang/rust-by-example#1300)
- eliminate the warnings (rust-lang/rust-by-example#1301)

## edition-guide

1 commits in 6601cab4666596494a569f94aa63b7b3230e9769..1a2390247ad6d08160e0dd74f40a01a9578659c2
2019-11-22 12:08:58 -0500 to 2019-12-29 10:40:55 -0800
- Updated install and uninstall instructions (rust-lang/edition-guide#194)

## embedded-book

1 commits in c26234930282210849256e4ecab925f0f2daf3be..9493b7d4dc97eda439bd8780f05ad7b234cd1cd7
2019-12-07 17:25:11 +0000 to 2019-12-27 20:05:00 +0000
- fixed typo in Interrupts.md  (rust-embedded/book#218)