Whitespace and trailing commas
Hide dependency behind a method
Inline one-liners
Apply DIY singleton-like behavior change to complexity calculator also
Whitespace
Extract superclass
Use instances, not classes, of calculators
Drop class only used in spec :O
Drop redundant specs, and the weird code they required
Drop "singleton-like" scaffolding
Push Forwardable down to subclass
Make a singleton-ish config instance available on demand
Flatten hierarchy

(That superclass wasn't really contributing much anymore.)