Feature idea: serialize from required CJS modules

Hi Blake,

I have a feature idea: serializing cross-file. Even with the `references` option enabled, requires/imports evaluate to their references (not the fully-serialized data).

Worse comes to worse, one could just bundle their code and then execute this lib's `stringify` fn. Although, ideally, this build step could go away.

[Here's a simple example](https://github.com/harrysolovay/javascript-stringify-issue-repro) of where this might come in handy.

Identifying the difference between node & browser environments seems to be a reason not to implement this... although I'm sure there're good workarounds.

Anyways, please let me know your thoughts on this. Would love to discuss implementations & work on a PR :)