classThis engine transitions from its initial state
'a engine_state -> Unixqueue.event_system ->
`Working 0in one step ("epsilon time") to the passed constant state. During this time event processing will continue, so concurrently running engines can make progress. For performance reasons, however, external resources like file descriptors are not watched for new events.
In previous versions of this library the class was called
However, this is not a constant thing. In particular, it is possible
that this engine is aborted, so the passed state is not reached.
To avoid programming errors because of the misnomer, this class has been