Compute Adler-32 hash on buf reader until EOF.

Example

use std::io::{Cursor, BufReader};
use simd_adler32::bufread::adler32;

let mut reader = Cursor::new(b"Hello there");
let mut reader = BufReader::new(reader);
let hash = adler32(&mut reader).unwrap();

println!("{}", hash) // 800813569