Add a new std feature, selected by default. This controls whether the
lib is built for no_std and uses features from std.
The const_fn_trait_bound feature is stable since Rust 1.61.0, so the
stable feature is left unused.
Allows building for no_std by disabling default features.
On x86, PIO does not use std and writing to /dev/port, and instead
always uses the IN and OUT assembly instructions.
cargo +stable build --release
cargo +stable build --release --no-default-features
cargo +nightly-2022-03-18 build --release --no-default-features --target x86_64-unknown-uefi -Zbuild-std=core