Stores passed in options in array serializers

This is supported in single serializers. This adds support for passing
options from array serializers to each serializer in it.

test/fixtures/poro.rb

@@ -78,6 +78,10 @@ PostSerializer = Class.new(ActiveModel::Serializer) do
   def blog
     Blog.new(id: 999, name: "Custom blog")
   end
+
+  def custom_options
+    options
+  end
 end
 
 SpammyPostSerializer = Class.new(ActiveModel::Serializer) do