bin/setup improvements

* Fix bug in foreman check
* Re-structure `bin/setup` to be more readable as more steps are added
* Add non-destructive (incremental) `.env` creator, with a twist<sup>[1]</sup>, borrowed from one of my projects.

See long-form messages in commits for more details.

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[1]: This one should probably be tested on Linux since some of the switches might be OS X / BSD specific.