Bump to Rails 4.0.2 in README
Do not care if frontend/backend/api cannot be loaded in extensions
Include display_price in variant return results
Variant#in_stock? now no longer takes a quantity. Call can_stock? instead

Variant#in_stock?'s method is now cached, too.
Cache currency settings on Spree::Money so that they're not loaded per call

It seems obvious in hindsight.