Add methods to hash usernames and emails with common random secret

So, this seems to work for what I need on MDN. I generate a secret as a random number, and use that to consistently hash usernames and emails across tables and databases. But, the secret is never stored or revealed, so hopefully that makes it anonymous enough

I also added some more logic to handle multiple files, and multiple databases within the same file.

Let me know if this looks insane or anything