Add the version protocol header

[flowersinthesand]

Now that the beta is over, it's time to version protocols, one for socket and one for each transport. Generally, version information is referenced in the handshaking so the protocol header would be proper.

• Add cettia-version w/ the initial value 1.0.
• Add cettia-transport-version w/ the initial value 1.0.

[flowersinthesand]

We need to set up a policy regarding protocol versions to deal with this issue. For now, the following should be enough:

• Given the server and the client, both implementation should work unless the major version is different.

It means that 1.1 server should behave as 1.0 server to work with 1.0 client and vice versa. It can be achieved by exchanging each implementation's protocol version when handshaking.

[flowersinthesand]

As for transport versioning, it will apply to only transports Cettia maintained, i.e. HTTP streaming and HTTP long polling except WebSocket.