Update to http4s-0.3.0

This updates to the latest http4s release available in maven central.

__Changes__
* Simplified server initialization
* Writable instance needed reworking
* Use the version of scalaz dragged along by scalaz-stream (7.1 I believe)

Thanks again for the cool demo. Do you mind if we link to it from the [http4s.org](http://http4s.org) website?