Added formulas for ntopng and ndpi

Dear all, please find enclosed the formulas for two open source tools ntop develops:
- nDPI: SDK for deep-packet inspection
- ntopng: web-based traffic monitoring application.

Thanks Luca Deri
`system` will already fail the test if its exit status isn't 0, so you can do:

```ruby
system "#{bin}/ndpiReader", "-i", "en0", "-s", "5"
```