Python cryptography, Rust, and Gentoo

> Rust not yet having reached critical mass to justify an alternative implementation

Rust is permissively licensed, which removes much of the motivation for any alternative implementation.

And personally, I'm hopeful that mrustc will meet any regulatory or similar requirements for "alternative implementation", so that we don't need another one for that reason either.

I hope that we go as long as possible *without* an alternative implementation, to avoid fragmenting the ecosystem by expecting crate authors to use the subset of Rust provided by that implementation.