Z-Stars 1.0 - 2014.07.09
    ★☆☆☆☆
    =====================
    
一个评论星星儿的sass函数

    核心部分 
    (需要浏览器支持 calc()属性，之后会增加自定义星儿及修复兼容性)
    -------------------------------------------------------------
    1★ == 10% * 2 ; 5★ == 100% ; - (letter-spacing/2) 间距差值
    循环出 .st-1 至 .st-10 名字; 
    .st-1{width:calc(10% - (letter-spacing/2));}
    .st-10{width:calc(100% - (letter-spacing/2));}
    -------------------------------------------------------------

    // 默认变量
    -----------------

    $solid:     ☆☆☆☆☆!default;
    $hollow:    ★★★★★!default;
    @mixin stars(
        $size:      14px,       //大小
        $color:     #f80,       //前景色
        $bg-color:  $color,     //背景色
        $spacing:   4px,        //间距
        $bg-icon:   $solid,     //背景样式
        $icon:      $hollow     //前景样式   
    ){
      ...
    }


    // sass
    --------------------
    .stars{
    @include stars($size, $color, $bg-color, $spacing, $bg-icon, $icon){
        // Add Style
    };
    }
    // css
    -------------------
    .stars {
    ...
    font-size: 14px;
    }
    .stars:before, .stars:after {
    ...
    color: #ff8800;
    letter-spacing: 4px;
    content: "☆☆☆☆☆"; }
    .stars:after {
    ...
    color: #ff8800;
    content: "★★★★★"; }
    .stars.st-1:after {
    width: calc(10% - 2px ); }
    .stars.st-2:after {
    width: calc(20% - 2px ); }
    ...

    // html
    ------------------
    <span class="stars st-1"></span>
    <span class="stars st-2"></span>
    <span class="stars st-3"></span>
    ...