Add full screen mode

[khawkins98]

It's fairly easy to add fullscreen support.

Just need two do two things:

1. add allowfullscreen to the iframe embed
2. add a bit of js that is fired on a button click (or such)

elm = document.getElementById("map");
elm.webkitRequestFullScreen();

More info at https://developer.mozilla.org/en-US/docs/Web/API/Element/requestFullscreen