DataSnapshot accepts multiple events (should not break existing code)
However, existing code might see a lot of QueueingEvent.OTHER's _iff_
this feature is utilized
Made AbstractSimpleFilter utilize multiple events per DataSnapshot
the DataSnapshot returned now contains a list of all the events that
happened since the last time a DataSnapshot was returned
Minor change to implementation of DataSnapshot
now contains an immutable list of QueueingEvent's, instead of generating
a new one immutable list out of a mutable list every time it is asked to
return the list