Add basic RangeReducer

Note: this modifies RangeAggregator to make matches() public.  If we want to leave it alone, we
will have to c/p the same code into RangeReducer since it is basically identical functionality

It also conflicts with the RangeAggregator stream, so has temporarily been renamed to "rangereducer"
Add basic MinReducer
Differentiate between internal and external type name
Add basic SumReducer
Add Cumulative Sum reducer prototype
Remove Cusum
Remove Linear/Weighted avg from Avg
Remove ArrayValue