Makes the use of the font-face simpler

With this implementation you have the bulletproof font code, and you only need to give parameters, not the complete src.

    @fonts: "/fonts/";
    @main-font-name: "Open Sans";
    
    .font-face(@main-font-name, @fonts, "open-sans-regular");
    .font-face(@main-font-name, @fonts, "open-sans-bold", 700);
    .font-face(@main-font-name, @fonts, "open-sans-italic", 400, italic);