Add support for IE<9 - Desktop only stylesheet

Please go easy on me, this is my first ever pull request.
Also, sorry for doing all this on the master branch, that's probably poor etiquette.

This amend creates a stylesheet for IE < 9 with no media queries, it takes the content which would be withing a width based media query and merely concatenates the styles. Creating a "Desktop Only" stylesheet.

Initiate this by creating a style-ie.scss containing:

```sass
$ie-mode: true;
@import "style";
```

And use it in your project like this.

```html
<!--[if (lt IE 9) & (!IEMobile)]>
<link rel="stylesheet" type="text/css" href="css/style-ie.min.css">
<![endif]-->
<!--[if gt IE 8]><!-->
<link rel="stylesheet" type="text/css" href="css/style.min.css">
<!--<![endif]-->
```

This is based on the work by Jake Archibald (@jakearchibald) here  - http://jakearchibald.github.io/sass-ie/