Does not implement `Read` and `Write` traits when built with no-std

[icefoxen]

Pretty sure there's no reason not to, since they're in core: https://doc.rust-lang.org/core/fmt/index.html

[icefoxen]

...my bad, I got fmt::Write and io::Write mixed up. No idea how I could have done that. :sweat: Still, it would be nice to implement fmt::Write so you could treat the thing as an output stream.