SNAPSHOT release. A bit of cleanup.
A naive, some might say overeager, eager-reducing-subscriber
Guard against zero flush-interval

not supported for eager-reducing-subscriber
eager-reducing-subscriber no longer overeager
Introduce EagerReducingSubscriberState record

and many internal changes to accomodate this strange new flavor of Subscribable.
Add ->eager-last-subscriber
Micro cleanup
Release 0.5.1