Function string_to_inv_letter_map 

pub const fn string_to_inv_letter_map(string: &'static str) -> LetterMapping

Creates a LetterMapping from a string that is the exact opposite of string_to_letter_map

Examples

let map = string_to_letter_map(foo);
let inv_map = string_to_inv_letter_map(foo);
let val = map[Letter::H];
assert_eq!(inv_map[val], Letter::H);