Stateful Processor

StatefulProcessor.init(handle)	Function that will be invoked as the first method that allows for users to initialize all their state variables and perform other init actions before handling data.
StatefulProcessor.handleInputRows(key, rows, ...)	Function that will allow users to interact with input data rows along with the grouping key.
StatefulProcessor.close()	Function called as the last method that allows for users to perform any cleanup or teardown operations.
StatefulProcessor.handleInitialState(key, ...)	Optional to implement. Will act as no-op if not defined or no initial state input.