Add an average button

[pmcelhaney]

As long as the cards aren't too far off, we take the average and use that as an estimate.

It would be great if the app calculated the average automatically. Will send a pull request when I get a chance. For now, here's a snippet of code I just threw together than can be pasted in the console.

var cards = $('.cards > div > div'); alert('Average is ' + Math.round(cards.reduce(function (a, b) { return {innerText: (+a.innerText||0) + (+b.innerText||0)}; }).innerText / cards.length))

PS - Thank you for making this app. Very well done and useful!