title: Siddhi Window does not expire matched events
body: <p>siddhi has an option named window that has many types: time, batch and ... . I need A sliding time window that holds events that arrived during the last windowTime period at a given time, and gets updated for each event arrival and expiry. also, it expires current events after any output even before window time end. window.time() is good but does not satisfy last part of my requisites and does not expire current events until window time ends. how can do this?</p>