Refactored MergingQueue to use method names more similar to the Java
collections
Removed assertion and comments
Cosmetic refactor
Done away with the whole idea of having two strategys, one to copy
events and advance immediately, and one to advance only when fully
consumed.

Swap this feature for capturing the sequence number of each event. After
processing of each, update the sequence. 

This approach I think is simpler.
Provide the current sequence to the MergeEventHandler