Exposing EVP_BytesToKey function

This function allows to derive a key and a IV using a salt, but I guess it isn't widely used since it's been deprecated in PKCS#5v2 in favor to PBKDF2 key derivations.
I needed it for generating and recalling an IV using the derived key as the input data.
You can find the doc of that function [here](http://www.openssl.org/docs/crypto/EVP_BytesToKey.html).

I didn't find any "official" test inputs, so I used a self generated one, but you have to take my word for it regarding its validity ! (:

Thanks !
Agreed. Will update the pull request.