Fix memory leak with multiple WebSocket servers on the same HTTP server

[nazar-pc]

My use case involves several WebSocket servers on the same HTTP server that each care about specific path in URL (for instance, one handles ws://localhost/ws1 and another ws://localhost/ws2).
In this scenario I do not want to reject request if it doesn't correspond to particular WebSocketServer's path. However, if I do not accept and do not reject request, it will be kept in memory even after original socket connection is closed entirely.

One workaround is to use wsServer.handleRequestResolved(request);, which is not a public API and not intuitive.

I decided that at least when socket is closed, request should be removed from memory.

BTW, I'd also like to see request.ignore() method that allows to clean memory earlier (without explicitly accepting or rejecting the whole connection), but in either case, this PR is a last defense from memory leaks in mentioned and similar scenarios.

[nazar-pc]

Can someone look at this, please?

[nazar-pc]

Can someone finally review this?

[ibc]

I'm afraid this project is not being maintained for a while. Trying to contact @theturtle32 to assign new maintainers with NPM permissions.