Thanks @JonRowe. I committed the consolidation of the two `each`s into one. As for the rest, well ... naming is hard :) `filter` in other langs (e.g. Clojure, Javascript, etc) means "return the matching things", but in this case it means "return everything but the matching things", so unless I go look at the `filter` method, I don't understand what `parse_options` is doing.

Same logic goes for `per_config`. It's still using the word "config", which means a `Configuration` object other places in this very file, whereas here it refers to what we're calling "options" elsewhere in this file. I think the explicit reference to the diff options file tells a better story.