mongoid/mongoid — pull request #3399 by arnkorty (2013-11-18 05:12:31+00:00)
Title: Add support for once persist many embedded documents with parent document

Before you only can once persist on embedded document with parent document.
Now add support for can once persist many embedded documents with parent documents.
```ruby
class User
include Mongoid::Document
embeds_many :items
end

class Item
include Mongoid::Document
field :name,type:String
embedded_in :user
end
# you can persist many embedded documents such as
User.create.items.create([{:name => 'foo'},{:name => 'bar'}])
User.create.items.create!([{:name => 'foo'},{:name => 'bar'}])
```