groupByKey and window aggregation in Trident

[Manu Zhang]

Hi,

I'm writing an Trident application calculating uservisits in sliding
windows. The current flow is to group uservisits by IP and then count over
windows but the problem is `GroupedStream` doesn't have a window function.
I'm not sure `groupBy("ip").toStream().window` is the right way to go. Any
documentation and examples will be very helpful.

Thanks,
Manu Zhang