Loop labels are not mentioned

[Seeker14491]

It's mentioned in the first edition and in Rust by Example, but not in the current book. This was mentioned in #994, but I don't think it was fixed.

[qrpnxz]

continue is also not mentioned.

[steveklabnik]

f22dace was the commit that moved the new features appendix into the text. That talks about breaking with a value, but doesn't use a label.

Continue is mentioned twice in passing. It could also use a better treatment.

[equal-l2]

Any progress on this?
I think breaking to a label is more important and more used than breaking with a value.
(Actually, I have used breaking to a label but I've never used breaking with a value)

[carols10cents]

Any progress on this would appear on the issue.