connection error handling: unsupported version, unsupported transport, bad handshake method

[biryukovmaxim]

In case of request contains unsupported transport or version, the server replies with code and message according
protocol

Code | Message
-- | --
0 | "Transport unknown"
1 | "Session ID unknown"
2 | "Bad handshake method"
3 | "Bad request"
5 | "Unsupported protocol version"

[Totodore]

That's great !

Could you add some unit tests for the custom errors ?

[biryukovmaxim]

That's great !

Could you add some unit tests for the custom errors ?

Sure, I will

[biryukovmaxim]

@Totodore
also I added handling of "unknown session id" and "transport mismatch", but that's not easy to write unit tests for them, I think it should be covered by integration tests

[Totodore]

Merging :). If later you wan't to start adding integration tests don't hesitate.