isogram, two-bucket: use second-edition links

[petertseng]

We forgot to apply #368 to
#378 and
#375.

[coriolinus]

There are some Markdown redundancies here, where we include lines which aren't rendered. I only specifically marked them for the isogram example, but the comments apply to both files.

I think we should decide whether to use inline or footnote-style links, and then stick to it.

[coriolinus]

It looks like the links are expressed both in footnote form and inline. I'm pretty sure this is redundant: if we have an inline link of the form [link_text](https://...), we don't need to include a footnote with the link's value. Contrariwise, if we want to use the footnote style, then the place where the link is actually used should look like [Modules][modules].

[coriolinus]

This footnote isn't referenced at all, and is stripped out of the rendered document.

[petertseng]

Correct on both counts, but not applicable to this PR.

[coriolinus]

Just saw that these changes were applied by a script. Fair enough; there's no reason to add manual work to generated output. I withdraw my objection.

[petertseng]

However, it is a true statement that those can be removed. I would simply remove them. Only question is whether https://doc.rust-lang.org/book/second-edition/ch14-00-more-about-cargo.html is needed. I took a < 5 second glance and made a snap decision of "no", but obviously a more reasoned decision should take priority over the five second decision.