interfaces as algebraic data types where applicable

[ransomw1c]

with the last iteration of this comment (on getArchivePathComponents) being elided from the source and yet another instance of "let's use interfaces to represent sum/union types!" enthusiasm appearing in my commentary elsewhere, i'd like to have the vestiges of this link trail (into github comments, into git history) referenced from the issue tracker.

so i am doing just that! creating a spin-off issue here and resolving this comment immediately.

Originally posted by @ransomw1c in #402