"The Rust Programming Language," Take II

An updated version of https://github.com/rust-lang/rust/pull/19461

This version vendors aturon/rust-book@731f7bf and builds it when building the docs. This is almost great, except my `make`-foo is poor, so I have my own personal paths in `mk/docs.mk`. How should I best get around that?

/cc @brson 
Agreed.

> On Dec 18, 2014, at 21:22, Alex Crichton <notifications@github.com> wrote:
> 
> In src/rustbook/LICENSE-APACHE:
> 
> > @@ -0,0 +1,201 @@
> > +                              Apache License
> We could probably avoid adding a new license.
> 
> \
> Reply to this email directly or view it on GitHub.
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