Transport type and Protocol Version info for Socket

[Totodore]

Adds the following function to the Socket struct:

• transport_type to get the current TransportType of the socket
• protocol to get the current ProtocolVersion of the socket in the case of multiple protocols enabled

Now handler extractors are implemented for TransportType and ProtocolVersion so now it is possible to use them as Handler arguments:

use socketioxide::{SocketIo, TransportType, ProtocolVersion, extract::*};

let (_, io) = SocketIo::new_svc();
io.ns("/", |socket: SocketRef, transport: TransportType| {
    assert_eq!(socket.transport_type(), transport);
});

io.ns("/", |socket: SocketRef, protocol: ProtocolVersion| {
    assert_eq!(socket.protocol(), transport);
});

Fix issue #177