expose option without crypto-browserify

[aulneau]

in looking through the code, I was surprised to see crypto-browserify is included by default.

It'd be nice to expose an option that does not include this by default. I think a big advantage of this kind of library is that it's proving native options for crypto apis, if folks need the crypto-browserify functionality, it should be more explicit.

[raphaelheinz]

I would also support this feature request. Are there any plans to exclude crypto-browserify? We use this package to rely on native operations so we don't need the overhead.

[boorad]

fixed in #264