js-duk: Implement input events

Replaces bind(K_BIND_INPUT, ...).

    function handler(ev)
    {
            switch (ev.type) {
            ...
            case "input":
                    line = ev.data;
                    mw.print("You inputted: " + line);
                    mw.say("⭐ " + line + " ⭐");
                    return false; // Suppress normal processing
            ...
            }
    }
    mw.onevent.push(handler);