add util to print benchmark runs to tsv file

[squito]

I love how complete the analysis of Distribution is, but sometimes I just want to export the runtimes to pull into an external tool, eg. for making a boxplot with R. TsvPrinter makes that easy.

[Ichoran]

Something like this is probably a good idea, but I won't have time for a couple of weeks to think about how to do it properly. In particular, hard-coding just runtime seems like maybe not the most useful thing to do, and I don't think embedding R output will necessarily scale all that well (people may want other tools supported). I'll get back to it on the 5th of July or so.