Stylus `font-smoothing` mixin

font-smoothing-mixin.styl

// Allows setting the font-smoothing option for styling better fonts. Font
// smoothing is specially valuable with custom fonts depending on the background
// color. Accepted values are none, antialiased, subpixel-antialiased.
//
// Usage:
// font-smoothing: antialiased;
//
// Compatibility untested.
font-smoothing() {
  if current-property {
    -webkit-{current-property}: arguments
    if arguments == antialiased {
      -moz-osx-{current-property}: grayscale
    } else if arguments == subpixel-antialiased {
      -moz-osx-{current-property}: auto
    }
    {current-property}: arguments
  } else {
    error('font-smoothing() must be used within a property');
  }
}