Syntax highlighting

Added syntax highlighting support with [highlight.js](http://highlightjs.org). 

Allows you to use any of the highlightjs styles listed [here](https://github.com/isagalaev/highlight.js/tree/master/src/styles). You have to put JUST the name, look at the example below.

Usage Example
```javascript
Blog.config.settings({
  syntaxHighlighting: true,
  syntaxHighlightingTheme: 'github'
});
```
You could put whatever you want in the theme so long as it is valid from the above URL. 
such as: ```atelier-dune.dark```
And that should highlight your code with the github.min.css from the CDN.

Fixes #73