The Event stream event handled to Lambda
http://docs.aws.amazon.com/lambda/latest/dg/eventsources.html#eventsources-ddb-update
EventRecord stores information about each record of a DynamoDb stream event
DynamoDbStreamRecord represents a description of a single data modification that was performed on an item
in a DynamoDB table.
TimeWindowEvent represents an Amazon Dynamodb event when using time windows
ref. https://docs.aws.amazon.com/lambda/latest/dg/with-ddb.html#services-ddb-windows
TimeWindowEventResponse is the outer structure to report batch item failures for DynamoDBTimeWindowEvent.