fix NullStatsd

make it an actual class
timer() can get called with 2/3 args
deal with inconsistently spaced datapoints

graphite may quantize datapoints
(i.e. with minutely resolution, x:47 gets stored at x:00)
but influx does not.
combine this with uneven spacing (metrics not being at step intervals,
but sometimes step+4 or step-4) then there was a bug where the algorithm
would get stuck on a bad point.
Now we advance when needed, see explanation in code.
fix wildcard behavior