Rollup of 9 pull requests

[frewsxcv]

• Successful merges: Papercut #40312, Extract book into a submodule #40332, clean up visuals on error index #40425 #40502, rustbuild: Don't hardcode 'nightly' for Cargo #40515, Stabilize pub(restricted) #40556, fix innacuracy in mir TerminatorKind::SwitchInt docs #40576, travis: Add timestamps to all build messages #40605, Fix typo in ptr doc #40667, config.toml.example: nightlies.txt got removed #40681
• Failed merges:

[rust-highfive]

Thanks for the pull request, and welcome! The Rust team is excited to review your changes, and you should hear from @nikomatsakis (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 Due to the way GitHub handles out-of-date commits, this should also make it reasonably obvious what issues have or haven't been addressed.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.

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[frewsxcv]

@bors r+ p=10

[bors]

📌 Commit c1b30c3 has been approved by frewsxcv

[bors]

⌛ Testing commit c1b30c3 with merge f2db6a8...

[bors]

💔 Test failed - status-travis