Suggested Changes (sessions, queuing, json bodies)

Had a moment free to implement the suggested changes:

* added sessions via session-cookie
* added queuing and batch-sending of updates from client to server.
* changed from form-encoded update bodies, to json.

I was of two minds about whether to send the session cookie in response to the request for the html file, or the gif file.  Not sure it matters much either way, but if you'd prefer to have it sent with the GIF, let me know.

Re the final suggestion (queuing and sending of server -> client messages in update responses) -- sounds good.  We'll need to chat about how these messages get produced from the connection.