The current implementation of SpringBootKinesisEventHandler only handles
non-aggregated events. Attempting to process aggregated events caused
ungraceful failure.
This commit fixes that by de-aggregating any events before performing
conversion. Non-aggregated events are still handled transparently.
In addition, detection of Message<T> input is performed, and
output messages are wrapped accordingly.
User can extend SpringBootApiGatewayRequestHandler instead of the
generic SpringBootRequestHandler. It ties the code to AWS and the
API Gateway, but at least it supports the incoming data fully.
Fixes gh-111, closes gh-136
