Add crypto:pbkdf2_hmac/5 BIF to the crypto module

[Bryan Frimin]

Hello everyone,

I propose to add the pbkdf2_hmac/2 function to the crypto module.

PBKD2 with HMAC is used by a lot of applications and libraries in
Erlang, currently, most of it uses the basho one or a fork of the basho
one.

As Erlang already binds OpenSSL and because this function is available
even on the OpenSSL 0.9.8c, I think it can be a great UX improvement to
have it from the OTP instead of an external library.

It's why I suggest enriching the crypto module with this function. I've
already opened a pull request[1].

I tried as much as possible to follow the contribution guide. Don't
hesitate to tell me if I made a mistake somewhere.

[1] https://github.com/erlang/otp/pull/5421

Regards,

-- 
Bryan Frimin
https://www.frimin.fr
bryan@REDACTED