This removes "side" and "msgnum" from the URLs, and puts them in a JSON
request body instead. The server now maintains a simple set of messages
for each channel-id, and isn't responsible for removing duplicates.
The client now fetches all messages, and just ignores everything it sent
itself. This removes the "reflection attack".
Deallocate now returns JSON, for consistency. DB and API use "phase" and
"body" instead of msgnum/message.
This changes the DB schema, so delete the DB before upgrading the server.
This roughly parallels the way that blocking/eventsource.py and the pypi
"requests" modules work: the server can set the encoding (with
"Content-Type: text/event-stream; charset=utf-8"), and the EventSource
parser will decode accordingly. However eventsource_twisted.py *always*
returns unicode (on both py2/py3), even when the server hasn't set an
encoding. blocking/eventsource.py returns bytes (on py3, and str on py2)
when the server doesn't set an encoding.
In the future, eventsource_twisted.py should return bytes when the
server doesn't set an encoding.
eventsource_twisted.py includes an alternate approach that might be
necessary (a to_unicode() function instead of always using .decode), but
I won't be sure until enough of Twisted has been ported to allow the
EventSourceParser to be tested.
Also fix demo.py for python3.
The main wormhole code is str (unicode in py3, bytes in py2). Most
everything else must be passed as bytes in both py2/py3.
Keep the internal "side" string as a str, to make it easier to merge
with other URL pieces.
