New graphs for tsv-utils performance benchmarks

[Jon Degenhardt]

A small thing - Many people who have seen the performance 
benchmarks for eBay's TSV Utilities find the text table format 
I've used in the past hard to read. Me too. So, I finally 
generated more traditional graphical representations for the 2018 
benchmark results.

The graphs are here: 
https://github.com/eBay/tsv-utils/blob/master/docs/Performance.md#2018-benchmark-summary

There are no new benchmarks, just new visualizations of the 
results.

For folks who not familiar with these benchmarks - This is part 
of performance studies done by comparing eBay's TSV Utilities 
with a number of command line tools providing similar 
functionality (e.g. awk). The results shown were presented at 
DConf 2018.

* Details of the performance study - 
https://github.com/eBay/tsv-utils/blob/master/docs/Performance.md
* DConf 2018 talk slides - 
https://github.com/eBay/tsv-utils/blob/master/docs/dconf2018.pdf