Update Rouge and fix CSS class bugs

Incorporates #41
[See the changelog](https://github.com/Arcovion/middleman-syntax/blob/6854f1ca8c4934724cb59b69f8d7f752f23b5b33/CHANGELOG.md) for more details and explanations.
Note the failing specs are due to #38 
I also changed the version number here which I probably shouldn't have; just wanted to write the changelog update myself :P

This patch also automatically joins the CSS class and language together if the chosen CSS class ends with a dash, allowing further compatibility with [the HTML5 spec](http://www.w3.org/TR/2011/WD-html5-author-20110809/the-code-element.html). Could use a `lang_prefix: 'string'` option instead, or just allow any prefix with <code>```prefix-lang</code> and give the suffix to the lexer.
What do you think is the best way to handle the prefix?