A single data point in a time series.
.. attribute:: interval
The time interval to which the data point applies. For
GAUGE metrics, the start time is optional, but if it is
supplied, it must equal the end time. For DELTA metrics,
the start and end time should specify a non-zero interval,
with subsequent points specifying contiguous and non-
overlapping intervals. For CUMULATIVE metrics, the start
and end time should specify a non-zero interval, with
subsequent points specifying the same start time and
increasing end times, until an event resets the cumulative
value to zero and sets a new start time for the following
points.
