[Pod] Include subspec dependencies

Closes #62

No tests, because: https://github.com/CocoaPods/search.cocoapods.org/blob/trunk-database-rewrite/spec/lib/models/pod_spec.rb :scream: 
I don't know that they will be looking for that _specific pod_, but I think it's information that shouldn't be thrown away (and will also allow searching for a fully qualified subspec name `RestKit/Network` to yield the pod)