An IndexBar for HTML
- please go to see the demo, it's easy for you!
| container | {string} IndexBar容器的选择器描述符，必填 |
| callback | {function} 切换序号时回调function(key){} |
| keys | {string|array} 显示的索引字符，默认'ABCDEFGHIJKLMNOPQRSTUVWXYZ' |
| maxScale | {number} 目标字符的最大缩放比例，默认为4 |
| offset | {number} 字母偏移系数，默认为8 |
| direction | {string} left|right|top|down 字母突出方向，默认left(其他方向尚未实现) |
| color | {string} 字体颜色，默认#000 |
| activeColor | {string} 选中的序号文本的颜色，默认#39f |