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

[Undiscussed Horrific Abuse, One Victim of Many]

here's my half-implemented proposal:

sv.satoshi.io s t
xsha256=f43a3b0fe7be10206074a8cf565671a4960f616d2b56ce4b66a6e100383b2b8a

the existing code keys into the first letter of each word, so I
introduced the letter 'x' to indicate a certificate fingerprint and
maybe let it be more backward compatible.