All this does is parse the regexes out of the config file.
I've vendored libregexp from Bellard's quickjs project, because it's
reasonably small and self-contained, and POSIX regexes don't support
captures. We're eventually going to want captures for URL rewrites, so
this'll do for now.
We'll later want to set these on the SSL object (rather than SSL_CTX),
so move these into the host struct for later access.
We'll prefer to set it on the SSL object so that we can automatically
use an up-to-date certificate, per ~sircmpwn/gmni#26.
