summarize: missing aggregations

[avereha]

There is list of aggregation supported by graphite: https://github.com/graphite-project/graphite-web/blob/master/webapp/graphite/functions/aggfuncs.py
We are missinng: avg_zero, stddev, range- and rangeOf, multiply.

[avereha]

This also raises the question: what should we use for this list of aggregations? The documentation or the implementation?