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)

Usage Example
```javascript
Blog.config.settings({
  syntaxHighlighting: true,
  syntaxHighlightingTheme: 'github'
});
```
And that should highlight your code with the github.min.css from the CDN.

Fixes #73