Closes rust-lang#29540

Originally, this was my 30 minute introduction, and we eventually made
it the opener to the book. But as rust-lang#25918 has shown, the example I use
here has some issues. The good news is that Rust makes heap allocation
syntatically expensive, but the bad news is that that means showing
equivalent programs from Rust and other languages is difficult. After
thinking about it, I'm not sure this section is pulling its weight, and
since it has problems, I'd rather just pull it than try to re-write it
right now. I think the book is fine without it.

FIxes rust-lang#25918

in favor of just expect()

Fixes rust-lang#29506

This comment was leftover from an earlier revision of a PR, something
that never was merged. There is no ZST special casing in Vec::drop.

Fixes rust-lang#28824

Closes rust-lang#29540

r? @huonw

Rustdoc pages with a search box inadvertently override `ctrl-s` in addition to the intended `s` and `S` keys.  You can test this in at least Firefox and Chrome (tested: Windows): press `ctrl-s` on http://doc.rust-lang.org/std/.  The search box is focused when instead the browser's save feature should be activated.  This PR fixes `ctrl-s` and possibly other browser shortcuts.

Originally, this was my 30 minute introduction, and we eventually made
it the opener to the book. But as rust-lang#25918 has shown, the example I use
here has some issues. The good news is that Rust makes heap allocation
syntatically expensive, but the bad news is that that means showing
equivalent programs from Rust and other languages is difficult. After
thinking about it, I'm not sure this section is pulling its weight, and
since it has problems, I'd rather just pull it than try to re-write it
right now. I think the book is fine without it.

FIxes rust-lang#25918

in favor of just expect()

Fixes rust-lang#29506

vec: Remove old comment in Vec::drop

This comment was leftover from an earlier revision of a PR, something
that never was merged. There is no ZST special casing in Vec::drop.

Fixes rust-lang#28824

Thanks.
r? @steveklabnik

r? @steveklabnik