First stab at adding ngrep

I'm not sure what to call the licence; it seems to be the BSD licence
with a few clauses about attribution added (which I *think* we're
complying with)

This has only been tested on Yosemite.

I'm guessing this will need some tweaking (the name of the license at least) before it can land.
The license seems to be `BSD-like` see https://en.wikipedia.org/wiki/Ngrep