Level 3 - ???

Since we have a model and a view, we only need interactivity in the form of update and subscriptions.

We need to subscribe to two things:

1. Keyboard presses
2. Ticks at some interval for our game loop

Remember also that the subscriptions function takes the current model as an argument, so if the snake is dead there is no need to subscribe to anything!

The following functions will prove useful

• every : Float -> (Posix -> msg) -> Sub msg

• Browser.onKeyDown : Decoder msg -> Sub msg

• Create the Msg type

• Create the update function
• Create the subscriptions function