Use mdbook-linkcheck

[pickfire]

https://lib.rs/crates/mdbook-linkcheck

It seemed better integrated with mdbook and uses the existing flow, mdbook build.

[KappaDistributive]

Note that this will also require updating mdbook to at least version 0.3.0.

[pickfire]

I wonder if there is still a maintainer for rust cookbook.

[KappaDistributive]

@AndyGauge is still around -- don't worry.

As it is the nature with these side projects, attention/activity will fluctuate.

[AndyGauge]

I won't rewrite the build scripts to use a different link checker, but will accept a PR that correctly moves to a rust solution.

[pickfire]

I tried doing this but looks like the link checker implementation is quite different and there are some stuff that is not valid (I also found broken links at https://rust-lang-nursery.github.io/rust-cookbook/web/clients.html). I got confused on what how the link works, the error is pointing to some random place.