[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 phrased my question the wrong way around. I should have said: who searches for a pod via the subspec name? Are there many cases where you just know the subspec name but not the pod name? I don't mind adding it, but am wondering if this case is one that occurs often, or at all.