rate calculation options
added the ability to specify rate calculation options when performaing a query. specifically the query can indicate if the metric on which the rate is being calculated is a counter, what the roll over value for that counter is, and what is a reset threshold for the counter. the reset threshold is a value that if the calculated rate exceeds it is reasoned that an anomaly occurred and the calculated rate is returned as 0.0.
Merge branch 'master' of https://github.com/davidkbainbridge/opentsdb