Add coming soon placeholder page for 2.0.x site

This replaces the homepage with a coming soon placeholder page. Keeps a short description of hapi and adds a link to the 2.0.x API reference.

Screenshot:

![screen shot 2014-01-16 at 9 36 49 am](https://f.cloud.github.com/assets/808159/1933073/314f0244-7ed5-11e3-9f6b-ea0e90ab386d.png)

/cc @hueniverse @wpreul