Enhance Series-Analysis to compute statistics from the NBRCNT line type.

[JohnHalleyGotway]

This is a request from Rachel North from the UK Met office made to Lindsay Blank during HWT 2019. Rachel and Marion Mittermaier would like to plot Fractions Skill Score spatially. It would be pretty straightforward to enhance Series-Analysis to support NBRCNT statistics in the output_stat flag, like this:

output_stats = { ... nbrcnt = [ "FSS" ]; }

We'd also need migrate the "nbrhd" dictionary from the Grid-Stat config file over to Series-Analysis.

We need identify priority and funding for this work.

[TaraJensen]

Charge 2702691

[mpm-meto]

This is a sample plot from the Woodhams et al 2018 paper....