scrypt node binary seems unneeded and very painful

[sullivanpt]

Do you mind if I make a PR to swap out scrypt.js in favor of just using scryptsy? Since this library is supposed to be geared toward web development (true?) it doesn't seem to make sense to include a server side only dependency like scrypt.

If I'm overlooking some server side use case and we need to maintain the binary scrypt dependency for performance, then would you be opposed to making scrypt an optional dependency? (I can try to make a PR for this to scrypt.js, not sure it will be non-breaking though).

Thanks for the feedback.

[sullivanpt]

Seems like many downstream dependencies like ethereumjs-wallet also have a requirement on scrypt.js. I moved the PR to axic/scrypt.js#3