Implemented `.font-face` and cache busting support.

Created by: roelvanhintum

I added a font-face mixin which is usefull for implementing web fonts. I use this on multiple projects and i tested it on: Firefox, Chrome, Safari, IE8+

Example usage:

.font-face(Font, font-regular, e('path/to/font/'), normal, normal);
.font-face(Font, font-italic, e('path/to/font/'), normal, italic);
.font-face(Font, font-bold, e('path/to/font/'), bold, normal);
.font-face(Font, font-bolditalic, e('path/to/font/'), bold, italic);

Usage for the bold-italic variation of the font in CSS would look like:

font-family: 'Font';
font-style: italic;
font-weight: bold;