Add Jekyll 2.0.0 release post.

/cc @benbalter – would love your :eyes: before we release.

- [x] Sell the new features, don't just list them
- [x] List contributors
- [x] Be even more nostalgic about the release date

![screen shot 2014-05-05 at 3 05 59 am](https://cloud.githubusercontent.com/assets/237985/2875685/bdd8d232-d423-11e3-959b-257c8debf9a6.png)

#2166