Implement framing protocol

[doronguttman]

see: http://sockjs.github.io/sockjs-protocol/sockjs-protocol-0.3.3.html#section-42

SockJS client accepts following frames:

• o - Open frame. Every time a new session is established, the server must immediately send the open frame. This is required, as some protocols (mostly polling) can't distinguish between a properly established connection and a broken one - we must convince the client that it is indeed a valid url and it can be expecting further messages in the future on that url.

• h - Heartbeat frame. Most loadbalancers have arbitrary timeouts on connections. In order to keep connections from breaking, the server must send a heartbeat frame every now and then. The typical delay is 25 seconds and should be configurable.

• a - Array of json-encoded messages. For example: a["message"].

• c - Close frame. This frame is send to the browser every time the client asks for data on closed connection. This may happen multiple times. Close frame contains a code and a string explaining a reason of closure, like: c[3000,"Go away!"].

Framing accepted by the server

• SockJS server does not have any framing defined. All incoming data is treated as incoming messages, either single json-encoded messages or an array of json-encoded messages, depending on transport.