Methodes principales
Safer optionnal parameters management
Services configuration
Correction du parametre expected sur deleteItem
Tests DynamoDb Client
Implementation of remaining methods.
README update with DynamoDb informations.
Add proxy class
Events management + service definition
Cache interface
Merge branch 'feature/dynamodb' into feature/sqs

Conflicts:
	README.md

src/M6Web/Bundle/AwsBundle/DependencyInjection/M6WebAwsExtension.php
	src/M6Web/Bundle/AwsBundle/Event/Command.php
	src/M6Web/Bundle/AwsBundle/Resources/config/services.yml