Added Xkcd Me Message Handler

Thank you for the continued opportunity to work on this. I created an Xkcd Me Message Handler so that we can enjoy the fun and wisdom of Xkcd using NBot.

![shoot_for_the_moon](https://f.cloud.github.com/assets/2660739/1608856/bcfab32c-551a-11e3-975a-0fd7b643d802.png)