Add support for HdrHistograms

[nathanielc]

HdrHistograms are High Dynamic Range Historgrams. The idea is that they can represent histograms with an arbitrary number of significant digits in precision or a certain range of values.

The data structure is quite simple https://github.com/codahale/hdrhistogram/blob/master/hdr.go#L29 and can be merged/aggregated with other instances. As a result HdrHistograms can be aggregated along time or other dimensions.

It should be possible to represent a single histogram as a single record in a wide table. We need to investigate how facilitate collection of HdrHistograms and storing them in InfluxDB. But once that is solved Flux should be able to aggregate them and produce quantiles based on them.

[nathanielc]

I wonder if we should update https://github.com/influxdata/platform/pull/685 to be more generic as to the representation of the histogram so that the function can consume either linear/log histograms or hdr histograms. Alternatively we could create an hdrHistogramQuantile function as a separate entity.