HTTP/1.x and DNS demultiplexer

 hddemux listens on a stream and routes incoming clients to either an
 HTTP/1.x backend or a DNS stream-based backend depending on the first
 request to appear on the stream.
 .
 This is useful when making DNS-over-TLS (RFC 7858) connections that
 appear to the network be HTTPS connections, for example, which makes
 it easier to traverse a network that would prefer to block the user
 from making DNS-over-TLS queries.