Demos need compiled CSS from the project to work

In order for the demos in the iframes to display properly, they need a compiled version of the CSS from the project inside the documentation's output folder.

Currently, I'm solving this by having grunt compile the CSS and copy it to my output folder - but I think DocJS should handle it automatically.

Perhaps it can be added as a config variable:

```
demoStyles: '/folder/less/styles.less'
```

When generated, DocJS grabs this file, compiles it, moves it to the output folder, and updates the demo files with the correct CSS ref.