Tracking issue for `std::ascii` reform (RFC 486)

[aturon]

Tracking issue for std::ascii reform (RFC 486)

[aturon]

cc @SimonSapin

[SimonSapin]

I’ve published the removed functionality in an ascii crate on crates.io, after modernizing the API a bit. The source is at https://github.com/SimonSapin/rust-ascii

However, I am not planning on maintaining this crate further or keeping it up-to-date with language changes. I will happily give maintainership to whoever wants it.