Inconsistency between `hash_into` function names

[brxken128]

There's multiple differently named functions that all do the same thing - hash a password into a buffer:

• argon2: .hash_password_into()
• balloon-hash: .hash_into()
• bcrypt-pbkdf: .finalize_into() (this one is understandable as it can be incremental)
• scrypt: it's the only option available, via scrypt()
• sha-crypt: does not provide the functionality at all

I personally think the easiest solution would be to rename balloon-hash' .hash_into() into .hash_password_into(), and although it'd be a breaking change it would unify the function names a little more.