Fix off-by-one highest memory address

[baskerville]

In the context of the stack/heap example (1 GiB of RAM), the highest possible memory address is 2^30 - 1.

Correlated minor fixes/enhancements:

• Use the correct, standardised, term for 2^30 bytes: a gibibyte.
• Replace <sup>x</sup> by ^x^ (pandoc translates the latter to the former).

r? @steveklabnik

[rust-highfive]

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[steveklabnik]

Even though "gibibyte" is technically correct, nobody actually uses it, so I'm not sure this is actually an improvement.

We don't use pandoc to render the docs, did you verify this renders correctly?

[baskerville]

• I can understand the will to use popular terms, but the problem is that one gigabyte is 10^9 bytes.
• I made an incorrect assumption, sorry about that. This feature is probably only available in pandoc's variant of Markdown. I tried to build trpl only but I couldn't find the appropriate target: there's a docs target but it builds the whole documentation and seems to take ages to complete.

Since there's multiple ways of fixing the off-by-one error, I think I would rather create an issue for this and let the Rust team decide on how to address it.

[steveklabnik]

make trpl should build the book.

And yeah, thanks! Did you hear that we're going to end up with the book published? I'll be interested to hear what my editor thinks.

Did you end up opening that issue, or did I miss it?