Update `Making Pong` for elm 1.0.0

Hi,

I doing the [Making Pong](http://elm-lang.org/blog/Pong.elm) tutorial the other day and had to make some changes to get it working with Elm 1.0.0.

I did the following to get it to work:
 * change `type` to `type alias`,
 * change `data` to `type`,
 * change `toText` to `fromString`
 * change `show` to `toString`
 * and change `lift` to `Signal.map`