Function cookie_factory::pair

pub fn pair<F, G, I>(first: F, second: G) -> impl SerializeFn<I> where
    F: SerializeFn<I>,
    G: SerializeFn<I>, 

applies 2 serializers in sequence

use cookie_factory::{length, pair, string};

let mut buf = [0u8; 100];

let len = {
  let (len, _) = length(pair(string("abcd"), string("efgh")))(&mut buf[..]).unwrap();
  len
};

assert_eq!(len, 8usize);
assert_eq!(&buf[..8], &b"abcdefgh"[..]);