Replace tempdir by tempfile

[Eijebong]

The former has been deprecated in favor of the latter

[Eijebong]

I didn't include a version bump in there because I don't know what the right thing to do is (since it's in an alpha version and all :p).
It would be nice to have this released quickly as it's one of the last thing that's keeping winapi 0.2 in rustc

[Michael-F-Bryan]

Thanks for the PR @Eijebong, I never noticed that tempdir has been deprecated.

I didn't include a version bump in there because I don't know what the right thing to do is

The tempdir crate is just an internal implementation detail of mdbook and not exposed anywhere, so there's no need for a version bump.

It would be nice to have this released quickly as it's one of the last thing that's keeping winapi 0.2 in rustc

Works for me. It looks like you forgot to update a bunch of things in the tests/ directory, but as soon as all the tests pass again we should be good to merge.

[Eijebong]

Yup, I'm on it ^_^ forgot to check that cargo test was compiling

[Eijebong]

There we go