Initial import of raw TCP and UDP echo helpers

It should say "ooni-probe meter" instead of "ooniprobe test". In general ooni-$SOFTWARE_COMPONENT is used when referring to the software name. ooni$SOFTWARE_COMPONENT is used when referring to the executable that is installed on the unix based system of the user.

*Note to self: these conventions should be written somewhere clear.* We even had a ticket about this at some point: https://trac.torproject.org/projects/tor/ticket/7462, though they have slightly changed since.