Function mid_string 

pub fn mid_string(prev: &str, next: &str) -> String

Create a string that is lexicographically halfway between the left and right strings

Examples

use midstring::mid_string;

assert_eq!(mid_string("aaa", "aaz"), "aan");
assert_eq!(mid_string("abc", "abcab"), "abcaan");

assert_eq!(mid_string(&String::from("abcde"), "abchi"), String::from("abcf"));

let left = String::from("abc");
let right = "abcab".to_string();
let should_be = String::from("abcaan");
assert_eq!(mid_string(&left, &right), should_be);