Add Podspec for the RouteGuide proto library

objective-c/route_guide/RouteGuide.podspec

+Pod::Spec.new do |s|
+  s.name     = "RouteGuide"
+  s.version  = "0.0.1"
+  s.license  = "New BSD"
+
+  s.ios.deployment_target = "6.0"
+  s.osx.deployment_target = "10.8"
+
+  # Base directory where the .proto files are.
+  src = "../../protos"
+
+  # Directory where the generated files will be place.
+  dir = "Pods/" + s.name
+
+  # Run protoc with the Objective-C and gRPC plugins to generate protocol messages and gRPC clients.
+  s.prepare_command = <<-CMD
+    mkdir -p #{dir}
+    protoc -I #{src} --objc_out=#{dir} --objcgrpc_out=#{dir} #{src}/route_guide.proto
+  CMD
+
+  s.subspec "Messages" do |ms|
+    ms.source_files = "#{dir}/*.pbobjc.{h,m}", "#{dir}/**/*.pbobjc.{h,m}"
+    ms.header_mappings_dir = dir
+    ms.requires_arc = false
+    ms.dependency "Protobuf", "~> 3.0.0-alpha-3"
+  end
+
+  s.subspec "Services" do |ss|
+    ss.source_files = "#{dir}/*.pbrpc.{h,m}", "#{dir}/**/*.pbrpc.{h,m}"
+    ss.header_mappings_dir = dir
+    ss.requires_arc = true
+    ss.dependency "gRPC", "~> 0.5"
+    ss.dependency "#{s.name}/Messages"
+  end
+end