Python cryptography, Rust, and Gentoo

I don't know why the neovim-gtk authors bumped their MSRV but most likely they saw some small feature that would be useful, and view upgrading the compiler as a trivial step (`rustup upgrade`), and so saw it as an easy win. If upgrading the Rust compiler is actually hard for some significant part of their community (I don't know why that would be), let them know!