[Request] Example of customizing the session

[bkuhl]

Would you be able to add an example on how to customize one or two of the session settings using SessionFunc in the ./examples directory? I've been tinkering with it for a bit and can't get it to work.

[bkuhl]

I was able to disable discordgo's underlying tracking of everything which was consuming ~13GB of RAM on the 92k servers my bot was connected to. After disabling tracking usage went down to ~400MB. Here's how I disabled tracking:

func main() {
    // other bot code

    manager := dshardmanager.New("Bot " + token)
    manager.SessionFunc = customizeSession

    // other bot code
}

func customizeSession(token string) (*discordgo.Session, error) {
    s, err := discordgo.New(token)
    if err != nil {
        return nil, errors.WithMessage(err, "customizeSession")
    }

    // Don't store any messages in the history
    s.State.MaxMessageCount = 0

    // Disables all state
    s.StateEnabled = false

    // We don't need to track the state of anything with the servers we connect to
    s.State.TrackPresences = false
    s.State.TrackRoles = false
    s.State.TrackEmojis = false
    s.State.TrackMembers = false
    s.State.TrackVoice = false
    s.State.TrackChannels = false

    return s, nil
}