After reading the whole changeset, I'm (at least initially) a :-1: on extracting this `dirs` object. I think it would take this PR—which would otherwise be a net-simplification—and ultimately makes both app & files configuration more visually (and keystrok-ily) cluttered. I think this is evidenced by the significant increase in the length of each line. 

I like to think we've struck a pretty good balance on conventionality vs configurability, and I think I need to be sold that giving users the ability to configure every directory's location is worth the costs. As I see it, those costs are:

1. Lineman's maintainers (us) will always have to remember to refer to those directories via their name in the file config object.
2. Lineman's users will have to tread carefully when approaching a new lineman project in the event that someone overrode a conventional directory path, perhaps for no reason but taste.

I think I could be swayed on either of the above costs if there was a really compelling case for overriding these directory locations. But even then, perhaps only for those particular directories we foresee the need.