Link to rustdoc page in the Rust book directly

[caspark]

No point sending people to a page which just says "this is now part of
the Rust book" (that page being http://doc.rust-lang.org/rustdoc.html).

[rust-highfive]

Thanks for the pull request, and welcome! The Rust team is excited to review your changes, and you should hear from @alexcrichton (or someone else) soon.

If any changes to this PR are deemed necessary, please add them as extra commits. This ensures that the reviewer can see what has changed since they last reviewed the code. The way Github handles out-of-date commits, this should also make it reasonably obvious what issues have or haven't been addressed. Large or tricky changes may require several passes of review and changes.

Please see CONTRIBUTING.md for more information.

[steveklabnik]

Thank you!

[steveklabnik]

@bors: r+ 4038694 rollup

[bors]

⌛ Testing commit 4038694 with merge 1f34e21...

[bors]

💔 Test failed - auto-mac-32-opt

[Manishearth]

run doc-trpl-compound-data-types [i686-apple-darwin]
running 18 tests
test _14 ... ignored
test _1 ... FAILED
test _13 ... ok
test _10 ... ok
test _12 ... ok
test _15 ... ok
test _0 ... ok
test _11 ... ok
test _16 ... ok
test _3 ... ok
test _17 ... ok
test _6 ... ok
test _5 ... ok
test _2 ... ok
test _4 ... ok
test _8 ... ok
test _7 ... ok
test _9 ... ok
failures:
---- _1 stdout ----
error: could not exec the linker `cc`: unknown error
error: aborting due to previous error
thread '_1' panicked at 'Box<Any>', /Users/rustbuild/src/rust-buildbot/slave/auto-mac-32-opt/build/src/libsyntax/diagnostic.rs:151

Looks like an intermittent?

[caspark]

Given this PR only changes docs (without tests), I think that failure must be unrelated to this PR.

[steveklabnik]

Yup, not your fault.

[alexcrichton]

@bors: retry