`sizeof` should be `size_of`

We'll bring this back in with the next commit, as a submodule.

It's all in the external repository now.

These pages will help people who have links to the older book.

Becuase I had run a `x.py doc` before doing this work, I had
accidentally relied on some files existing in places that they didn't
need to be.

This is for coordinating with our publishers; we don't ever want to test it.

Some links needed adjustment to support this new scheme.

The unstable book, libstd, libcore, and liballoc all needed some
adjustment.

Instead, stage0.txt got introduced.

See also commit 02538d4

…sakis

Implement `?` in catch expressions

Builds on rust-lang#39921. Final part of rust-lang#39849.

r? @nikomatsakis

Papercut

r? @steveklabnik

…ichton

Extract book into a submodule

Part of rust-lang#39588

We probably don't want to land this till after the beta branches on friday, but would still ❤️ a review from @alexcrichton , since I am a rustbuild noob.

This pr:

1. removes the book
2. adds it back in as a submodule
3. the submodule includes both the old book and the new book
4. it also includes an index page explaining the difference in editions
5. it also includes redirect pages for the old book URLs.
6. so we build all that stuff too.

r? @alexcrichton

clean up visuals on error index rust-lang#40425

r? @steveklabnik

Knocking these down to a smaller header made it look quite nice in my opinion.

…r=petrochenkov

Stabilize pub(restricted)

Fix rust-lang#32409

…po, r=nikomatsakis

fix innacuracy in mir TerminatorKind::SwitchInt docs

Each index of `values` corresponds to an index of `targets`, and `targets` additionally has a "default case" element at its end, so `targets.len() == values.len() + 1`, not the other way around. For example, [here](https://github.com/rust-lang/rust/blob/0aeb9c12979e6da753701a798d04105b6b1a8c28/src/librustc/mir/mod.rs#L549-L550) is a concrete instance of `SwitchInt` being constructed with `targets.len() == 2` and `values.len() == 1`.

Fix typo in `ptr` doc

`sizeof` should be `size_of`

…sxcv

Add missing urls in Option enum

r? @rust-lang/docs

…alexcrichton

config.toml.example: nightlies.txt got removed

Instead, stage0.txt got introduced.

See also commit 02538d4

Add missing associated type Item to Iterator