[New Pod] ProtobufObjC

Objective-C wrappers around google's protobuf binary serialization format.
From the defacto canonical git repo https://github.com/booyah/protobuf-objc .

This is basically the same pull request as https://github.com/CocoaPods/Specs/pull/51 , but with JUST ProtobufObjC.

Still no reply on tagging a version :(