Adding support for outputting results as csv

[Keating950]

I found it useful to export results so that I could drop outliers from the comparison, so I modified the script to optionally output results to a .CSV file. I figured I would share my changes so that they could be integrated if you think they're up to par. All the best!

[thomasmerz]

@Keating950 , if you're interesting in regular tests and long-time analysis with fancy charts you might have a look at dnsping_rrd so you don't have to import it into Excel-like sheets and graph it by yourself 😁