emojify-parser proof of concept

# DO NOT MERGE THIS

This is a proof of concept that uses [emojify-parser](https://github.com/trevorah/emojify-parser), so that the emojify function only has to worry about dom manipulation.

To use with nodejs, you would have to use jsdom like this:
```javascript
jsdom.env('<span id="cat">hello :cat:</span>', function(err, window) {
  var el = window.document.getElementById('cat');
  emojify(el, { document: window.document });

  console.log(el.outerHTML)
  // '<span id="cat">hello <img class="emoji" src="/cat.png" title=":cat:" alt=":cat:" align="absmiddle"></span>'
});
```

Let me know what you think and whether or not I should carry on and make this fit for merging.