Compile with latest nghttp2
INTERNALS: nghttp2 must be 0.6.0 or later
Implement public key pinning

Option --pinnedpubkey takes a path to a public key in DER format
and only connect if it matches (currently only implemented with
OpenSSL).

Extract a public RSA key from a website like so:
openssl s_client -connect google.com:443 2>&1 < /dev/null | \
sed -n '/-----BEGIN/,/-----END/p' | openssl x509 -noout -pubkey \
| openssl rsa -pubin -outform DER > google.com.der