fix#949
* New error codes are introduced for WebSocket failures
* More verbose messages for error codes
* Error codes are mapped to conditions for ease of testing
* error::failed and error::handshake_failed are deprecated (don't use)
Actions Required:
* Code which explicitly compares error_code values against the
constant `websocket::error::handshake_failed` should compare
against `websocket::condition::handshake_failed` instead.
* Code which explicitly compares error_code values against the
constant `websocket::error::failed` should compare
against `websocket::condition::protocol_violation` instead.
fix#778
* The version data member is replaced with accessor
member functions.
Actions Required:
* Call member function message::version instead of accessing
the version member at call sites.
Vinnie Falco