提供本地储存LocalStorage的接口

使用方法

//获取某一项LocalStorage的值;
LocalStorage.getItem(key);

//设置某一项LocalStorage的值;
LocalStorage.setItem(key,value);

//移除某一项LocalStorage的值;
LocalStorage.removeItem(key,value);

//清空LocalStorage;
LocalStorage.clear();

//监视某一项LocalStorage值的变化;
LocalStorage.onstorage(key,callback);