Macro impl_write

macro_rules! impl_write {
    ($ty: ty, $write_fn: expr, $flush_fn: expr $(, $bounded_ty: ident : $bounds: path),*) => { ... };
}

Because we cannot provide a blanket implementation of std::io::Write for all implementers of this crate’s io::Write trait, we provide this macro instead.

This macro will implement Write given a write and flush fn, either by implementing the crate’s native io::Write trait directly, or a more generic trait from std for users using that feature. In any case, this crate’s io::Write feature will be implemented for the given type, even if indirectly.