Feature request: add an option to use litcrypt in constants/statics

[ph0llux]

It would be a very nice feature, to do something like this:

#[macro_use]
extern crate litcrypt;

use_litcrypt!("MY-SECRET-SPELL");

const VOLDEMORT: &str = &lc!("Voldemort");

fn main(){
    println!("his name is: {}", VOLDEMORT);
}

[anvie]

It's not possible to use const as the litcrypt need to decode string on-the-fly during runtime.