This is currently a copy of the `std::ascii` module
as of [Rust](https://github.com/rust-lang/rust/)
[66601647cd8050fb9a63a56d1b6a8d836a0eab39](https://github.com/rust-lang/rust/commit/66601647cd8050fb9a63a56d1b6a8d836a0eab39).
In the future, it will only provide the functionality
that is [moving out of `std::ascii`](https://github.com/rust-lang/rfcs/pull/486).