Better document what readiness to use

[Thomasdezeeuw]

For example a TcpListener what Ready value should it have when registering to get all events? Try to document that for each type.

[Thomasdezeeuw]

Or better provide a per type readiness, for example:

impl TcpStream {
    /// The advised interests to use when registering a `TcpStream`.
    const INTERESTS: Ready = Ready::READABLE | Ready::WRITABLE;

    // ...
}

This currently doesn't work since the or operator (|) isn't a constant function.

[Thomasdezeeuw]

What I currently use to get all events.

In net module:

• TcpListener: Ready::READABLE,
• TcpStream: Ready::READABLE | Ready::WRITABLE,
• UdpSocket: Ready::READABLE | Ready::WRITABLE,
• ConnectedUdpSocket: Ready::READABLE | Ready::WRITABLE.

In unix module:

• Receiver: Ready::READABLE,
• Sender: Ready::WRITABLE,
• Evented{Fd, Io}: depends on the file descriptor.