Provide combinators for creating/modifying foreign data

[paf31]

I find myself wanting inverses to read, more and more, especially now that foreign-lens exists.

[dvdsgl]

👍

I need a way to return complex PureScript values from my library to calling JavaScript code, and there's no canonical way for me to do this, from what I can tell.

[paf31]

My workaround for this has been to use arrays and records, and then call toForeign to turn that into a Foreign value. It's not ideal for various reasons though.

[puffnfresh]

I'll submit a PR for this.