Allow files to be hoisted when they are outside of package base (or simlink inside node_modules)

[CraigMason]

Hello,

It would be very useful to support asset emission for certain packages even if they are outside of the package base.

This is useful when working with local dev copies of modules with native code, as they can be symlinked into node_modules.

Maybe a white-list option.

https://github.com/zeit/webpack-asset-relocator-loader/blob/master/src/asset-relocator.js#L1129

Thank you