Support randomly-named directories about tempdir

[steveklabnik]

I may be missing something, but the argument to new is only a prefix, right? So it does this already. If you didn't want a prefix, you could keep it empty. https://doc.rust-lang.org/tempdir/src/tempdir/lib.rs.html#202

[Susurrus]

@steveklabnik Sorry! I skimmed the intro and didn't see the part that said that. And then I looked at the docs for new() and they didn't say anything about generating a filename randomly. That comboed with the fact that the argument isn't an Option<&str> is why I thought it didn't generate random directory names. Maybe the docs for new() can be extended to provide a little more details?

[KodrAus]

We've moved the tempdir API into tempfile. One of the changes was to remove the prefix argument from TempDir::new() and use a builder to specify a prefix/suffix so I'll go ahead and close this one now. Thanks all!