Add tool to find sybils based on fingerprints.
Add tool to find sybils based on fingerprints.

This is basically a reimplementation of the sybil checker which is part
of doctor:
<https://gitweb.torproject.org/doctor.git/tree/sybil_checker.py>

Since we make use of zoossh, we are able to parse archived consensuses
faster and as a result, it's more convenient to find sybil attacks which
happened way in the past.

NullHypothesis/sybilhunter