[spam][crazy] Adding Cert Pinning to E-X

[Undiscussed Horrific Abuse, One Victim of Many]

it's been years and nobody's implemented this!

right now i have a draft 'irc format' proposal that looks like:

sv.satoshi.io t s-sha256.f43a3b0fe7be10206074a8cf565671a4960f61

in the the code, a 'features' dict is used. i recall the protocol
might send 'features' around, although they might be flags rather than
strings.

anyway the nearness to a little normativeness gives me enough reason
to glance through ssl norms and see if there's a standard condensed
way to list fingerprints of a cert associated with their digests