Merge: Reworked crypto.nit to introduce basic XOR attacks

lib/crypto:
`crypto.nit` was getting pretty overwhelmed with the upcoming changes so it was exploded into a package.
Introduced classes for cipher management to help with attacks.

lib/crapto:
Introduced 2 attacks on basic XOR ciphers.

Pull-Request: #2080
Reviewed-by: Jean Privat <jean@pryen.org>
Reviewed-by: Lucas Bajolet <r4pass@hotmail.com>