Add @alfredxing to the @jekyll/core team.

Team post because he's awesome! :tada: 

![screen shot 2014-12-17 at 11 31 00 am](https://cloud.githubusercontent.com/assets/237985/5477432/35b8f746-85e0-11e4-9c57-3532fc612b2c.png)
I don't want to take any credit away from Alfred for incremental regeneration, but several of the things he used were from my initial code in the initial attempt. It seems incorrect to say that he single-handedly wrote it.