Rollup merge of rust-lang#72151 - ehuss:update-books, r=ehuss

Update books

## book

2 commits in e37c0e84e2ef73d3a4ebffda8011db6814a3b02d..6247be15a7f7509559f7981ee2209b9e0cc121df
2020-04-26 09:31:36 -0500 to 2020-05-03 10:55:09 -0500
- Fix guessing game listing explanation (rust-lang/book#2321)
- Update ch01-01-installation.md (rust-lang/book#2325)

## edition-guide

1 commits in 8204c1d123472cd17f0c1c5c77300ae802eb0271..49270740c7a4bff2763e6bc730b191d45b7d5167
2020-04-09 18:55:50 -0700 to 2020-05-11 08:50:29 -0500
- Use rust-lang/rust linkchecker on CI. (rust-lang/edition-guide#197)

## embedded-book

1 commits in 40beccdf1bb8eb9184a2e3b42db8b8c6e394247f..366c50a03bed928589771eba8a6f18e0c0c01d23
2020-04-26 17:44:14 +0000 to 2020-05-07 09:04:42 +0000
- Add HAL patterns/guidelines/recommendations  (rust-embedded/book#235)

## nomicon

3 commits in 4d2d275997746d35eabfc4d992dfbdcce2f626ed..d1517d4e3f29264c5c67bce2658516bb5202c800
2020-04-27 10:24:52 -0400 to 2020-05-12 13:47:00 -0400
- Rename Unique::empty to Unique::dangling
- Use simpler link syntax
- Replace catch_panic by catch_unwind

## reference

3 commits in ed22e6fbfcb6ce436e9ea3b4bb4a55b2fb50a57e..892b928b565e35d25b6f9c47faee03b94bc41489
2020-04-24 12:46:22 -0700 to 2020-05-11 11:13:51 -0700
- clarify that str data must still be initialized
- remove language-level UB for non-UTF-8 str
- Replace incorrect term "parent modules" with "ancestor modules". (rust-lang/reference#806)

## rust-by-example

2 commits in ffc99581689fe2455908aaef5f5cf50dd03bb8f5..ab072b14393cbd9e8a1d1d75879bf51e27217bbb
2020-04-24 15:05:04 -0300 to 2020-05-09 08:46:39 -0300
- Fix link of formatting traits (rust-lang/rust-by-example#1346)
- Remove stale footnote (rust-lang/rust-by-example#1345)

Author: RalfJung