Cleanup and unify access to request details

[andrejleitner]

There are socket.request.headers, socket.conn.request.headers and socket.handshake.headers all referencing the same thing, so this is just a suggestion for a clearer interface around request data.

Socket.IO server version: 3.1.0

https://github.com/socketio/socket.io/blob/3.1.0/lib/socket.ts#L126
https://github.com/socketio/socket.io/blob/3.1.0/lib/socket.ts#L587-L589
https://github.com/socketio/socket.io/blob/3.1.0/lib/socket.ts#L596-L598

[darrachequesne]

I think the official way is the handshake object: socket.handshake.headers.

We can indeed remove the other references (which were added a long time ago), but that will be a breaking change. We could schedule it for v4, what do you think?

[andrejleitner]

To decide what is the official way is probably up to you, I just vote for cleaner interface.
One way instead of three seems better to me ... also for users to understand.
The next major version makes sense.

[andrejleitner]

5.0.0?