Function hash1

code/chapter05/hash.rs:1–7

(ascii_str: &str,  size: usize)

fn hash1(ascii_str: &str,  size: usize) -> usize {
    let mut sum = 0;
    for c in ascii_str.chars() {
        sum += c as usize;
    }
    sum % size
}

// hash1 的迭代形式
fn hash_iter(ascii_str: &str, size: usize) -> usize {