last-mile latency measurements

What's Changed

• last-mile latency: scamper version by @jesteria in #32
• last-mile latency measurement: traceroute+ping version by @jesteria in #33

Shout-out

To @kyle-macmillan for work incorporated from #13.

Full Changelog: 0.0.1-rc.3...0.0.1-rc.4