Improve size-optimizing FAQ docs

[johnthagen]

A question that comes up fairly often (for example, recently on the User Forum), is how to reduce Rust binary sizes. This PR attempts organize the FAQ on this section in a way that helps a user actually enable all of these options, as well as update some out-of-date information.

[rust-highfive]

Thanks for the pull request, and welcome! The Rust team is excited to review your changes, and you should hear from @ashleygwilliams (or someone else) soon.

If any changes to this PR are deemed necessary, please add them as extra commits. This ensures that the reviewer can see what has changed since they last reviewed the code. Due to the way GitHub handles out-of-date commits, this should also make it reasonably obvious what issues have or haven't been addressed. Large or tricky changes may require several passes of review and changes.

Please see the contribution instructions for more information.

[johnthagen]

Closes #918

[frewsxcv]

Looks great to me, thanks! 📝

[frewsxcv]

cc @rust-lang/docs

[QuietMisdreavus]

Looks good, thanks so much! I do have one comment, though: Since #![no_std] binaries are recently stable in 1.30, could you also take a look at the "Standard Library" section farther down and see if you can update the sample Rust code to reflect that? It looks like the reference PR that adds information for #[panic_handler] has some sample code that uses the new features.

[johnthagen]

@QuietMisdreavus Could that be another PR? I am not as familiar with those features as I am with those that I submitted in this PR.

[QuietMisdreavus]

That's fine, this is good as-is.

[johnthagen]

Note, as it appears that the new website will no longer maintain this information, I have created min-sized-rust

[johnthagen]

Since this repo is effectively dead now, closing PR. See min-sized-rust for the latest information.