Implement `merge` and `mergeAll`

[Matan Lurey]

Reference: http://reactivex.io/documentation/operators/merge.html.

[Matan Lurey]

Actually, it's not clear this would be a transformer. Should it still go here? @natebosch

[Nate Bosch]

If we wanted to implement this as a StreamTransformer I think we could.

someStream.transform(merge(someOtherStream))

It looks like there are two variants in Rx. A static Observable.merge(source1, source2) and a method on observable instances. You can see both versions here: http://www.introtorx.com/Content/v1.0.10621.0/12_CombiningSequences.html#Merge

I think the transform(merge(someOtherStream)) implementation fits this package. I think the other approach wouldn't.