* remove isDemandAvailable
* hide emit from CompletionHandler context
* throw if more than one emit in response to an input
* had to remove the OrderedMerge test/sample because emitting
from CompletionHandler is currently not supported
* FlexiRoute and FlexiMerge might become more capable later, see issue 16753
* FlowMaterializer is now the actor independent interface
* ActorFlowMaterializer is the actor based interface
* MaterializerSettings renamed to ActorFlowMaterializerSettings
* impl.ActorBasedFlowMaterializer renamed to impl.ActorFlowMaterializerImpl
* Optimizations included in ActorFlowMaterializerSettings
* Note that http is using FlowMaterializer in api, but I suspect that it
will currently only run with a ActorFlowMaterializer
