Added atomic update example.

examples/atomic_updates.rb

@@ -0,0 +1,36 @@
+require 'pathname'
+require 'rubygems'
+require 'bundler'
+
+Bundler.require(:default)
+
+root_path = Pathname(__FILE__).dirname.join('..').expand_path
+lib_path  = root_path.join('lib')
+$:.unshift(lib_path)
+
+require 'toy/mongo'
+
+class User
+  include Toy::Mongo
+  include Toy::Mongo::AtomicUpdates
+
+  adapter :mongo_atomic, Mongo::Connection.new.db('adapter')['testing']
+
+  attribute :name, String
+  attribute :bio, String
+end
+
+user = User.create(:name => 'John', :bio => 'Awesome!')
+puts user.name # John
+puts user.bio  # Awesome!
+
+# simulate another process updating only bio
+user.adapter.client.update({:_id => user.id}, '$set' => {:bio => "Changed!"})
+
+user.name = 'Nunes'
+user.save # save performs update with $set's rather than full doc save
+
+user.reload
+
+puts user.name # Nunes
+puts user.bio  # Changed!