Serverless stack definition:
14-19 initializes the Vert.x instance. AWS Lambda will hold on to this instance for the life of the container/JVM. It is reused in subsequent requests.
17 registers the User Service handlers
22 defines the main handler method that is called when the Lambda function is invoked.
27 sends the Lambda function input to the (dynamic) address where handlers are waiting to respond.
44-66 defines the specific handlers and binds them to the appropriate channels (http method + resource path)
Serverless + Vert.x = BLISS