Fix a few links in the book

Links to directories and direct links to doc.rust-lang.org don't work properly
when viewing the docs offline so fix them.

src/doc/book/choosing-your-guarantees.md

@@ -232,7 +232,7 @@ indicator (one word in size) along with the data.
 
 At runtime each borrow causes a modification/check of the refcount.
 
-[cell-mod]: ../std/cell/
+[cell-mod]: ../std/cell/index.html
 [cell]: ../std/cell/struct.Cell.html
 [refcell]: ../std/cell/struct.RefCell.html
 

src/doc/book/documentation.md

@@ -76,7 +76,7 @@ This [unfortunate error](https://github.com/rust-lang/rust/issues/22547) is
 correct; documentation comments apply to the thing after them, and there's
 nothing after that last comment.
 
-[rc-new]: https://doc.rust-lang.org/nightly/std/rc/struct.Rc.html#method.new
+[rc-new]: ../std/rc/struct.Rc.html#method.new
 
 ### Writing documentation comments
 

src/doc/book/error-handling.md

@@ -2205,7 +2205,7 @@ heuristics!
 [3]: ../std/option/enum.Option.html#method.unwrap_or
 [4]: ../std/option/enum.Option.html#method.unwrap_or_else
 [5]: ../std/option/enum.Option.html
-[6]: ../std/result/
+[6]: ../std/result/index.html
 [7]: ../std/result/enum.Result.html#method.unwrap
 [8]: ../std/fmt/trait.Debug.html
 [9]: ../std/primitive.str.html#method.parse

src/doc/book/using-rust-without-the-standard-library.md

@@ -22,11 +22,12 @@ fn plus_one(x: i32) -> i32 {
 ```
 
 Much of the functionality that’s exposed in the standard library is also
-available via the [`core` crate](../core/). When we’re using the standard
-library, Rust automatically brings `std` into scope, allowing you to use
-its features without an explicit import. By the same token, when using
+available via the [`core` crate](../core/index.html). When we’re using the
+standard library, Rust automatically brings `std` into scope, allowing you to
+use its features without an explicit import. By the same token, when using
 `#![no_std]`, Rust will bring `core` into scope for you, as well as [its
-prelude](../core/prelude/v1/). This means that a lot of code will Just Work:
+prelude](../core/prelude/v1/index.html). This means that a lot of code will Just
+Work:
 
 ```rust
 #![no_std]

src/doc/book/vectors.md

@@ -152,5 +152,5 @@ API documentation][vec].
 [box]: ../std/boxed/index.html
 [generic]: generics.html
 [panic]: concurrency.html#panics
-[get]: http://doc.rust-lang.org/std/vec/struct.Vec.html#method.get
-[get_mut]: http://doc.rust-lang.org/std/vec/struct.Vec.html#method.get_mut
+[get]: ../std/vec/struct.Vec.html#method.get
+[get_mut]: ../std/vec/struct.Vec.html#method.get_mut

src/doc/nomicon/README.md

@@ -35,4 +35,4 @@ exception-safety, pointer aliasing, memory models, and even some type-theory.
 We will also be spending a lot of time talking about the different kinds
 of safety and guarantees.
 
-[trpl]: ../book/
+[trpl]: ../book/index.html