Rollup merge of rust-lang#63760 - ehuss:update-books, r=ehuss

Update books

## nomicon

25 commits in 8a7d05615e5bc0a7fb961b4919c44f5221ee54da..38b9a76bc8b59ac862663807fc51c9b757337fd6
2019-08-07 07:46:59 -0500 to 2019-08-19 10:04:32 -0400
- Fix transmute_copy link
- some edits
- drop parenthetical
- clarify dangling
- fix def.n of dangling
- fold uninit integer rule with reading uninit memory
- refactor null a bit
- resolve some nits
- raw ptrs must be initialized like integers
- Apply suggestions from code review
- explain when metadata is invalid
- mention !
- add more cases of UB
- avoid redundant UB
- stick to broader UB for raw ptr offsets/derefs for now
- be more precise about dangling
- subsume the NonNull things as library types
- handle recursion in the heading
- Define 'producing'
- NonNull, NonZero*
- list more ptr offset computations
- UB
- Fix typo in subtyping
- Add colon to `MySuperSliceable` too
- Fix typo `str::mem` to `std::mem`

## reference

2 commits in b4b3536..d191a0c
2019-08-07 02:29:50 +0200 to 2019-08-15 08:42:23 +0200
- Fix warning in stable-check (rust-lang/reference#653)
- our closure syntax comes from Ruby (rust-lang/reference#650)

## rust-by-example

5 commits in f2c15ba5ee89ae9469a2cf60494977749901d764..580839d90aacd537f0293697096fa8355bc4e673
2019-08-07 10:14:25 -0300 to 2019-08-17 23:17:50 -0300
- macros.md: Changing Sometime to more appropriate adverb form Sometimes (rust-lang/rust-by-example#1243)
- Add colon after "See Also" (rust-lang/rust-by-example#1242)
- Update enter_question_mark.md (rust-lang/rust-by-example#1208)
- Add destructuring bind examples (rust-lang/rust-by-example#1238)
- Change initial parameters in `fibonacci()` call. (rust-lang/rust-by-example#1241)

## embedded-book

1 commits in c5da1e11915d3f28266168baaf55822f7e3fe999..432ca26686c11d396eed6a59499f93ce1bf2433c
2019-08-05 23:02:10 +0000 to 2019-08-09 23:20:22 +0000
- semihosting: add comment adding feature flag to panic-semihosting  (rust-embedded/book#203)