Update books.

This required some changes in how the books are tested due to some changes in rust-lang/book.  It uses new syntax that is not compatible with bare `rustdoc --test`.  This changes it so that it uses rustbook to run the tests, which is essentially the same as `mdbook test`.

## reference

7 commits in 11e893f..64239df
2020-01-18 21:24:08 +0100 to 2020-02-10 19:05:13 +0100
- Update for nested receivers. (rust-lang/reference#724)
- clarify note re. leading `::` in 2018 (rust-lang/reference#752)
- Update macro-ambiguity.md (rust-lang/reference#754)
- typo fix: add missing `by` (rust-lang/reference#753)
- fix `TypeParamBounds` link on trait objects (rust-lang/reference#749)
- reorganize docs on references (rust-lang/reference#745)
- add MacroRepOp usage for ? (rust-lang/reference#744)

## book

49 commits in 87dd6843678575f8dda962f239d14ef4be14b352..6fb3705e5230311b096d47f7e2c91f9ce24393d0
2020-01-20 15:20:40 -0500 to 2020-02-12 13:48:57 -0500
- Fix nomicon links. (rust-lang/book#2253)
- Update to Rust 1.41.0 (rust-lang/book#2244)
- Listing 19-6: use ptr.add instead of ptr.offset (rust-lang/book#2201)
- Remove unneeded mutable reference
- Clarify deref coercion explanation
- Fix typo in link to 1.30 book
- Acknowledge Murphy's Law
- Clarify that buffer overread is UB in C
- Change from "must" to "idiomatic" about comments
- Fancy quotes
- Make HashMap types match previous example; add fwd ref to ch 13
- Tweak wording to array clarification
- Merge remote-tracking branch 'origin/pr/2236'
- Update all our crates (rust-lang/book#2235)
- Reword git caveat
- Merge remote-tracking branch 'origin/pr/2234'
- Merge remote-tracking branch 'origin/pr/2230'
- println! is a macro (rust-lang/book#2224)
- Update a translated version link (rust-lang/book#2221)
- move `Macro invocation` from section on tuple to section on mac… (rust-lang/book#2206)
- Do not limit `Self` usage in trait implementation (rust-lang/book#2197)
- Merge remote-tracking branch 'origin/pr/2191'
- Fix wrapping
- Merge remote-tracking branch 'origin/pr/2187'
- Updated appendix 07 to reflect deprecation of rustup install (rust-lang/book#2181)
- Make links to the Nomicon consistent
- Merge remote-tracking branch 'origin/pr/2180'
- Merge remote-tracking branch 'origin/pr/2175'
- Merge remote-tracking branch 'origin/pr/2171'
- Merge remote-tracking branch 'origin/pr/2170'
- Clarify and make consistent the explanation of unions
- Merge remote-tracking branch 'origin/pr/2166'
- Handle dev or test in the Finished output line
- Link to macros by example rather than macros (rust-lang/book#2164)
- Merge remote-tracking branch 'origin/pr/2147'
- Fix parens (rust-lang/book#2132)
- Clarify type inference with closures requires calling the closures
- Update link to French translation (rust-lang/book#2119)
- Merge remote-tracking branch 'origin/pr/2108'
- Add an explicit cross reference to data type
- Merge remote-tracking branch 'origin/pr/2105'
- ch15-02-deref: Improve explanation on immut-to-mut (rust-lang/book#2030)
- Remove unnecessary quotes
- Make markdown link identifier match
- Remove extra newline
- Merge remote-tracking branch 'origin/pr/2004'
- Extract code and output; script formatting and updating them (rust-lang/book#2231)
- Switch "Finally" to "Next" to reflect new chapters having been… (rust-lang/book#2098)
- ch19-06 added curly braces to macro output (rust-lang/book#2050)

## rust-by-example

2 commits in 1c2bd024d13f8011307e13386cf1fea2180352b5..32facd5522ddbbf37baf01e4e4b6562bc55c071a
2020-01-20 12:18:36 -0300 to 2020-02-11 09:25:06 -0300
- Add missing `dyn` in code sample (rust-lang/rust-by-example#1306)
- Improve grammar in a few sections (rust-lang/rust-by-example#1305)

## edition-guide

1 commits in 1a2390247ad6d08160e0dd74f40a01a9578659c2..37f9e6848411188a1062ead1bd8ebe4b8aa16899
2019-12-29 10:40:55 -0800 to 2020-02-10 14:36:14 +0100
- Fixed typo (rust-lang/edition-guide#196)

## embedded-book

4 commits in 4d78994915af1bde9a95c04a8c27d8dca066232a..b2e1092bf67bd4d7686c4553f186edbb7f5f92db
2020-01-14 08:25:25 +0000 to 2020-01-30 08:45:46 +0000
- Make typestate initialization notes correct  (rust-embedded/book#224)
- Mention discovery book more prominently  (rust-embedded/book#219)
- Replace nursery links with rust-lang links  (rust-embedded/book#222)
- Add a Glossary appendix page  (rust-embedded/book#223)

Fix displaying errors when rustbook tests fail.

This ensures that output from mdbook is displayed when running the rustbook wrapper. I believe this was a regression as a result of rust-lang#69115 where it was changed from running `rustdoc` directly to using rustbook.