Add minimal support for CSS pre-processed

Since this the webfont can be used with pre-processor (Sass (with Compass) or Less...), here are some littles changes to be able to produce pre-processor ready stylesheets (that does not need a rename)
FYI, I use it like that 
```js
        webfont: {
            icons: {
                src: '<%= happyPlan.src.assets.fontcustom %>/icons/*.svg',
                dest: '<%= happyPlan.build.assets.fonts %>/icons',
                destCss: '<%= happyPlan.src.assets.styles %>/components/fontcustom/icons/',
                options: {
                    styles: 'icon',
                    stylesheet: 'scss'
                }
            }
        },
```
But I test with many options (so created the htmlDemo parameter :+1: )