Website redesign

This is a complete redesign of the Clack website, with a couple extra additions. The changes are:

* Add a news section, with an announcement of the 1.0 release.
* Tutorial moved to Markdown, for easier maintenance and writing.
* Adds a section on reporting security issues (This is important considering that last issue with directory listings).
* Uses [highlight-lisp](https://github.com/orthecreedence/highlight-lisp) for syntax highlighting (You might notice some issues when rendering class names delimited by angular brackets, I've already reported this bug).

It looks like this:

* [Home page](http://i.imgur.com/kyYfQQb.png)
* [Tutorial](http://i.imgur.com/yKsYvR8.png)
* [News blog post](http://i.imgur.com/9KTeHRi.png)