This relates to #8, and explores using a single encoded header to
simplify parsing of more complex parameters from the server.
Spike towards server-controlled immediate printing.
I haven't been able to test this using my Arduino, because the FTDI cable I have at home is busted.
It's actually quite unlikely that I'm going to support this, at least in the basic Arduino sketch, since HTTP header parsing is so hard. That wouldn't stop more sophisticated clients (like the Raspberry Pi one) from supporting it though.