`keypress` event is deprecated

[emilgoldsmith]

Hi! I just wanted to highlight that the keypress event has been deprecated as can be seen here: https://developer.mozilla.org/en-US/docs/Web/API/Document/keypress_event

I know the Elm philosophy is all about best practices and not letting users shoot themselves in the foot, so thought I'd highlight it, though it would of course be a big breaking change to remove it from the API. As can be seen above MDN warns that this feature could be stopped being supported at any time (though with the history of backwards compatibility in the web world it's probably unlikely)