Add support for SNI proxies

[killerrabbit]

I've seen an increase in SNI proxies.

These proxies work by connecting to the domain indicated in SNI when connecting to a server and proxying the TLS connection to that domain through the proxy IP. Most are only for port 443, but if your ircd listens on port 443, or you have any cgiirc blocks(for things like mibbit, kiwiirc, etc.), they can use them to connect.