Erlang NIF for scrypt

An Erlang NIF for Colin Percival's "scrypt" function. It uses dirty CPU schedulers for
generating hash, leaving main schedulers for Erlang applications.

General information about scrypt can be found in these slides (PDF)
and Colin Percival's page on scrypt.

This library uses code from scrypt 1.3.1.

Using the library

Add library as dependency in rebar.config

{deps, [
    {erlscrypt, "1.0.0"}
    ...
]}.

Add scrypt as application dependency

{application, app,
     [
      {applications, [
                      ...
                      scrypt
                     ]},
      ...
     ]}. 

Use scrypt:scrypt/6 for encrypting data.