describe what's _actually_ in the payload of a relay begin cell

   To create a new anonymized TCP connection, the OP sends a

   RELAY_BEGIN data cell with a payload encoding the address and port

   of the destination host.  The stream ID is zero.  The payload format is:

         ADDRESS | ':' | PORT | '\000'

   where ADDRESS may be a DNS hostname, or an IPv4 address in

         NEWSTREAMID | ADDRESS | ':' | PORT | '\000'

   where NEWSTREAMID is the newly generated Stream ID to use for

   this stream, ADDRESS may be a DNS hostname, or an IPv4 address in

   dotted-quad format; and where PORT is encoded in decimal.

   Upon receiving this packet, the exit node resolves the address as