Add scrypt and argon2 as hash method
According to https://medium.com/analytics-vidhya/password-hashing-pbkdf2-scrypt-bcrypt-and-argon2-e25aaf41598e, PBKDF2 has not aged well,BCrypt is still good but there are better: SCrypt and Argon2. SCrypt is available in stdlib since Python 3.6 so it is a good default choice. Argon2 is even better but it requires an extra library so we should use only if it is available. So I propose to use by default this preferred order (if available): argon2, scrypt, bcrypt and pbkdf2_sha512.