A mixin to dynamically generate ::before syntax for icons.

Pseudo Before Icon

@mixin before-icon($icon, $icon-hover:false) {
  position: relative;
  z-index: 1;

  &:before {
		content: '';
		@extend .icon-#{$icon};
		display: block;
		height: icon-sprite-height($icon);
		left: 0;
		margin-top: -(icon-sprite-height($icon)/2);
		position: absolute;
		top: 50%;
		width: icon-sprite-width($icon);
		z-index: -1;
  }

  @if($icon-hover) {
  	&:hover {
  		&:before {
	  		@extend .icon-#{$icon-hover};
	  	}
  	}
  }
}