enoji to ignore <code> tags

All this time we blamed [emoji-images](https://github.com/HenrikJoreteg/emoji-images) when it was __emoji-skype__ that is replacing our code with images. I know __emoji-images__ still have the same problem, but I am not sure what would be your preferred approach to fix that, fork the repo? 

regarding this PR , I, desperately, tried multiple ways using regex only, even [asked SO](http://stackoverflow.com/questions/21372302/regexp-to-ignore-everything-between-code-and-pre-tags) for hAlp, but never got to a perfect FULL <code> ignore with regex only -- if you or anyone on the team is a regexp freak, I would love to see that solution.

So anyways, I modified one of the answers a little bit after performance testing, and included it here.

Also, till a perfect solution sees the light, there is no *solid* need to ignore `<pre>` tags since `marked` always, either produces an *inlined* `<code></code>` or a `<pre><code></code></pre>`