Re-opening deprecating Option::unwrap and Result::unwrap

In several programs, I've taken to writing safety comments on my uses of arithmetic operators.

Arithmetic is pretty much the most dangerous thing you can do in safe Rust (EDIT: not counting I/O or other similar interactions with the environment outside the program) – you need a lot of reasoning about the program to know that it isn't going to give you a panic or the wrong result.

(Note that wrapping is actually often a worse outcome than panicking, because the program will continue running but using the wrong numbers.)

Be kind of nice if we added some then. To be very very clear: I don't think just adding a warning is a complete solution... and it's a bit of a straw man to respond to that position.