Rollup merge of #47753 - steveklabnik:update-book, r=alexcrichton

Update book

This PR does two things:

1. update the book to include https://github.com/rust-lang/book/pull/1088
2. update to mdbook 0.1

Both of these things are big changes, so I want to land them now, well before the next branch, so we can kick the tires.

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Locally, I'm seeing some weirdness around the reference and this:

![image](https://user-images.githubusercontent.com/27786/35411917-8dcbb31a-01e8-11e8-8c30-0bd280d93b9d.png)

Putting this PR up so others can try and build and see if it reproduces for them.

2 files changed, 0 insertions, 0 deletions

diff --git a/src/doc/book b/src/doc/book
-Subproject 194eb8d5f1753fb5f4501011cebdc1b58571247
+Subproject a645960fe48946153936dd5628df4a90bd83798
diff --git a/src/doc/reference b/src/doc/reference
-Subproject 1d791b55b23ec5389fbd5b3cee80db3f8bbdd16
+Subproject e6a5d5d10aa2fde0baed7b29bf672bd9f3af896