Make it possible to use an IP address as a front (no DNS request and no SNI)

meek puts one domain name on the "outside" of your connection (the DNS request and SNI), and a different name on the "inside" (the HTTP Host header). It would be good for some uses if the outside could be just to an IP address rather than a domain name, so that there were no DNS request, and no server_name extension in the CLientHello. Kind of like if you were to browse to https://38.229.72.16/ instead of https://www.torproject.org/.

The motivating use case is using a CDN as a front instead of www.google.com. A CDN has many domains behind it, but if we choose just one of them as the front, that domain might get blocked (because the collateral damage would be limited to just one domain). Such blocking would break the transport and also incidentally get the innocent third-party domain, who has nothing to do with any of this, censored even for non-circumventors. What we want is to use one of the CDN's frontend IP addresses as a front, so that the censor has to block the whole IP and the thousands of domains behind it, not just a single domain.