Support conversion from &String to Slice

[carlsverre]

related to fjall-rs/fjall#99

[marvin-j97]

I thought Rust would use the From<&str>, because when you have:

fn f(s: &str) {}

let a = String::new();
f(&a); // this works

But apparently not

Edit: Yeah, this needs a manual deref:

struct ByteView(String);

impl From<&str> for ByteView {
    fn from(value: &str) -> Self {
        Self(value.into())
    }
}

fn f<T: Into<ByteView>>(v: T) {
    let bv = v.into();
}

pub fn main() {
    let a = String::new();
    f(&*a); // only this works
}

[carlsverre]

Yea, unfortunately it doesn't seem to trigger the implicit deref for From impls.