Proxy Lambda input and output format

[sihil]

It would be great to have objects that match up with the input and output formats documented at http://docs.aws.amazon.com/apigateway/latest/developerguide/api-gateway-set-up-simple-proxy.html#api-gateway-simple-proxy-for-lambda-input-format

[brackxm]

see https://github.com/awslabs/aws-serverless-java-container/tree/master/aws-serverless-java-container-core/src/main/java/com/amazonaws/serverless/proxy/internal/model

[asuresh8]

Added