cmd/gen-whitelist: investigate TLS certificate compression to improve generation speed

[adamdecaf]

#123 talks about how it's dreadfully slow to generate a whitelist from a modest collection of certificates. (30-40k on my local Firefox)

The RFC is still pretty early in its draft phase, but might be useful for round trip times when gathering up chains. I'm not totally sure as the protocol might be better for repeated handshakes with the same server and not that useful for sparse client -> host connection trees.

https://tools.ietf.org/html/draft-ietf-tls-certificate-compression-02